Rip-offs, known by economists as “market inefficiencies,” are cases in which the price of something has little to do with its actual value. They are particularly common in industries where oligopolistic conditions dominate, which has been increasingly common since deregulation fever hit Washington. In today’s marketplace, the consumer is often a sheep to be shorn. Here are seven common products where the buyer must beware.

1. College textbooks are a blatant rip-off.

As if kids trying to get an education don’t face enough financial hurdles, the textbook industry has found a way to soak them on every class. A $200 biology book? A couple of Benjamins for a math text that doesn’t even come with binding? That’s the new normal.

The National Association of College Stores reports that the average college student ends up paying about $655 for textbooksand supplies annually. That’s down a bit from $702 four years ago, but it’s still a big wad of cash.

All told, there’s been an 812 percent increase in the price of college textbooks since 1978. No, you didn’t misread that number. And you thought healthcare was going up!

Although speaking of healthcare, a student trying to pass a class is kind of like a patient trying to make it through surgery. You’re hardly a “consumer” who can shop for the best “products.” You do what your doctor or professor says. Don’t want to buy the book? Then you will not be passing the class.

You may recall buying used books in college or sharing and saving some money that way. But greedy textbook companies have found a way around that. They’ve rigged up access codes in new books that the student must use in order to do things associated with the class, like take an online quiz or turn in a homework assignment. The code can only be used one time, so the book loses a great deal of its usefulness after the semester.

Another trick the industry plays is to pump out new editions of exisiting books even when they aren’t justified. Or “bundling” various kinds of additional products, like special software, with the book. Kickbacks for professors who use certain textbooks—also known as bribes—have been widely reported.

The problem has gotten so bad that legislators are trying to come up with various ways to address it. California has committed to underwriting 50 textbooks for common undergraduate courses, which students worldwide will eventually be able to download for free via the California Digital Library.

2. Don’t fall for mattress scams.

Are icky little bugs filling up your bed? Oprah did a show on it. The Wall Street Journal warns that “the average mattress will double its weight in 10 years as a result of being filled with dead dust mites and their detritus.”

Eeek!

Cecil Adams over at Straight Dope looked up the claims, and found that scientists don’t buy it: “It’s nonsense,” said mite authority Larry Arlian, professor of biological sciences, microbiology, and immunology at Wright State University. “I don’t know where that originated. They’re not that prolific.”

Most people aren’t even allergic to dust mites, and there are ways of countering them, like putting impervious covers on mattresses and pillows, that don’t require shelling out thousands of dollars. The dust mite fear-mongering is just another way to get you to go shopping for something you may not need.

A mattress is a pretty boring product, so marketers and salespeople have to figure out all kinds of strategies to get you to replace them. They’ve thought long and hard about adding bells and whistles like extravagant covers, sleep numbers, and anti-bacterial green tea foam to justify high prices. You can easily spend several grand on a mattress.

The mattress industry features a system whereby retailers add on a giant markup, often 100 percent. This covers both sales commissions and lets stores announce a constant stream of “blow-out” sales. When you walk into a mattress store, the salesperson knows she pretty much has you. As the website Mattress Scam points out, people don’t really browse mattress stores for the heck of it, like they do clothing stores or electronic goods. You shop for a mattress when you think you actually need a new one. (Not many folks relish the idea of a secondhand mattress, with the recent bedbug scare.) Sellers charge high prices for a simple reason: They can get away with it.

Simple solution: Get a cover for the mattress you have, flip it around to keep it even, and vacuum regularly.

3. Tampons: the pay-as-you-flow rip-off.

If you are a woman reading this article, you will likely drop a couple thousand bucks on tampons in your lifetime. It is said that menstruating Americans go through an average of 11,400 tampons in their lives: That’s five tampons a day, five days a month, for 38 menstruating years.

Researcher Karen Houppert calls it “pay-as-you-flow.” When you see the various ways women get ripped off, you understand why. It may gall you, for example, to hear that unlike condoms, tampons and other sanitary products are taxed in many states. Yes, tampons are considered a luxury item instead of a necessity. When I was profusely bleeding during a recent trip to Brazil and couldn’t find a store, my situation certainly felt like a necessity! I’m sure you know the feeling.

Over the years, you may have noticed that the number of tampons in a box has dropped (from 40 to 32 in 1991, for example) while the price stayed the same. The major players in the tampon business, Procter & Gamble (Tampax), Playtex, Kimberly-Clark, and Johnson & Johnson, have well over 90 percent of the market, and under these oligopolistic conditions, they can pretty much do what they want. Excited by news of the growing global tampon market, tampon makers are focusing on “organic” products and snazzy, colorful wrappers.

I’m not going to sugarcoat this. There are alternatives, but they can be more, uh, hands-on. But if you’re ready to go bold, you could try washable pads, menstrual cups, and even sea sponges. Each has its upsides and downsides, and you have to be prepared for a bit more mess and effort.

4. The dark truth about printer ink.

It’s a classic marketing scheme. You sell one product, like a printer, at a rock-bottom price, essentially losing money. Then you turn around and sell everything else that you need to use that product at a giant markup. You may have gotten your printer cheap, but the ink and toner that make it work are super-costly.

The folks at MainStreet.com found some amazing research: “The website DataGenetics crunched the numbers and came to a shocking conclusion: Assuming a cartridge sells for $16.99, the 19 milliliters of ink it contains amounts to nearly $65,000 a gallon.” That is very likely the most expensive liquid you will ever purchase. The cost of one gallon of ink is the same as 2,652 gallons of gasoline!

Why the high prices? Like video game consoles, printers are loss leaders. You can get a PlayStation for a song, but the games are going to cost you big-time. Same thing with printers.

Here’s another fact: As David Robinson has reported at the Guardian, the amount of ink in individual cartridges has been gradually shrinking. Yep, the size of the sponges that hold the ink have shrunk and there’s basically just a bunch of empty space inside the cartridge.

And that’s not all. Much of the ink in your printer doesn’t even make it to the page. According to Consumer Reports, “it’s used to clean print heads and for other maintenance chores, typically when the printer is preparing to print after sitting idle for some time.”

If you don’t do a ton of printing, you might consider a slightly more expensive printer that won’t waste ink and will not break down. But if you’re going to be printing a lot, make sure you compare the cost of cartridges associated with different models. Also, if you print a lot, you may want to leave the printer on, because every time you turn it on you trigger that ink-wasting maintenance cycle.

5. Bottled water is a giant scam.

It’s become the accessory-of-choice for urbanites on the go. But here’s the reality: Bottled water is expensive, wasteful and probably not any healthier than tap water.

You may feel safe thinking that bottled water in the U.S. falls under the regulatory authority of the Food and Drug Administration. But in reality, as Chris Baskind reports, “about 70 percent of bottled water never crosses state lines for sale, making it exempt from FDA oversight.” And what is in that water? Who knows? There’s certainly no guarantee that your tap water is pristine (you can look up information on your own system here). But at least I can look up my water, which comes from the New York City System, and see how it is treated, read what violations have occurred, and review dates for follow-up actions. Can you do that on a bottle of water? No, you can’t.

Bottled water is thought to be exacerbating climate change. It produces heaps of waste that produces toxic fumes, and recycling possiblities are limited.

The proliferation of bottled water has also taken our focus off one of the great mainstays of public health: the construction and maintenance of safe municipal water systems.

6. Be careful choosing generics over brand-name products.

Sometimes generics are a money-saver, like prescriptions drugs, or over-the-counter medications, which are legally required to list their ingredients and adhere to the same standards as brand-name products. If you need a pain reliever, grab yourself the generic brand and save a buck.

Beyond medicines, lots of times there’s not much difference between generic and brand-name products. Often the very same item, like, Reynolds Wrap, can be found repackaged as house brands. In taste tests, consumers have a hard time telling the difference between, say, a name-brand ketchup and generic stuff. For drivers, gas is gas, so if you come across off-brand gasoline, don’t be afraid to buy it.

But generic is not always your best bet. Large chain supermarkets have started selling “second tier” brands that may be lower in quality, with names like “Kroger Value” and “Food Lion’s Smart Option.” This trend is on the upswing, so expect more products to fall under this category and be sure to check ingredients and pay attention to performance. Generic paper products, like paper towels, for example, have fewer fibers and don’t absorb as well, so you may end of using more of them. Generic paint may be watered down, so watch out for that one, too.

7. Don’t be fooled by germ-fighting supplements.

Every time I go to my gym, I see somebody fighting the war on germs, wiping down any equipment they touch with treated towelettes, and vigorously rubbing their hands. On the playground, moms and dads are continually swiping Junior with antimicrobial cleansers.

Scrupulous or stupid? Nobody wants to pick up a germ that will make her sick, but the multitude of products that claim to fight germs and boost the immune system don’t amount to much in the way of health. They are also a waste of money. In fact, some germ-fighting ingredients have been found to be toxic, like triclosan, which has been added to everything from toothpaste to makeup.

Ironically, the prevalence of these products may actually lead to hardier germs that will make more of us sick.

Want to avoid infection? Try basic hygiene, like washing your hands with good old-fashioned soap and water.