I think this is the case, most of the time, especially with older, perhaps out-of-print, books.

In some cases, with out-of-print stuff, you may have a small but steady demand for them, and that allows sellers to charge an arm-and-a-leg for them. I've personally noticed it with certain financial and health-related books that I had been recommended or seen recommended online. Fans of some online person all try to buy the same book, so demand is high enough to charge a high price.

Depending on how popular the 2012 Doomsday phenenom pans out this year, certain out-of-print or hard-to-find prep-related books could get very expensive this year.

Yet another reason might be that the sellers are not quite selling the same thing as each other. I just received a book this week that wasn't what I expected. This seller's price was only a fraction of everyone else's price for this out-of-print book. Normally, that's a bit of a red flag for a merchant I have never used before, but the total amount was minimal so I took the chance. Shipping was prompt, but instead of a normal paperback book, it was actually a bound set of copied pages. Similar to something I often had to buy in college for classes, but still, very well done and all the pages are clear and just as legible as the regular book. In this case, I'm not complaining because I save so much money, but it would've been a problem if I were buying a book as, say, a gift. I buy a lot of books online and this is the first time I have experienced this, though, so don't be put off my by story.

I was stiffed by a small, independent bookseller that I was using for the first time, but this happened only once to me. Never received my book. In that case, I had paid by PayPal. I complained to PayPal, explained what I had done to try and resolve the issue, and after PayPal investigated, PayPal refunded me the whole amount.

Besides PayPal, for peace of mind, using a virtual credit card number is a wonderful tool for online shopping. Different products may work slightly differently, but basically you log into your credit card company's website, generate a unique credit card number, and then use that to purchase something online. Typically, the number has a short expiration date and generally can only be used by one merchant. So even if a hacker stole the number at some point, they can't use it because the number is expired or because they are not the same entity as the merchant for who first used it. The hacker's attempt to use it is rejected by the credit card company. I do all of my online shopping and pay certain bills using virtual credit card numbers and I have never seen a fraudulent charge on any of my credit cards (currently use Citibank and Discover's virtual credit card services).

Here's a short article on them if you want to learn more.

Oh, by the way, if you're going to start buying things online, you might consider setting up a separate email address just for online purchases. Sometimes, you can get a lot of new solicitations or annoying spam messages after purchasing from certain merchants. You can just use a free web email account from any number of companies, like Yahoo or Hotmail.

And don't use the same password for every merchant! Set up a unique one for each website and keep track of them.

My parents were small business owners, so I certainly try to support local businesses, but online shopping really opens up a lot of possibilities that just aren't possible with brick-and-mortar stores. I'd say 99.9% of my online transactions have been just fine. Have fun!