I've been selling on eBay and Amazon since 2007 and hope to share some lessons I've learned along the way. The whole experiment began as a way for my husband to reduce his collection of 1,200 CDs. Listing media on Amazon is dead simple—type in an ISBN, click the "Sell Yours Here" button and follow the prompts.

Over just a few months, we sold and shipped dozens (maybe hundreds) of his CDs. Some sold for surprisingly high prices, including a UK remix of classic '80s song "Safety Dance" and Vols. 3 & 4 of Desert Sessions, a project of Queens of the Stone Age frontman Josh Homme.

The money was rolling in from selling these CDs that we already owned when we realized we were running out of things to sell! The next time we were at a thrift store, we flipped through the bookshelves, looking for things we thought might sell. I don't recommend just buying anything that "looks good" (as we started off doing) because too many books, especially best-sellers, sell for less than a dollar on Amazon. There are several excellent ISBN-lookup tools to help you choose appropriate books when you're out shopping.

Still, unless you have a fancy bar-code scanner and can process a whole bookstore quickly, your gut reaction is a big part of choosing which books to look up. As I said in the last paragraph, avoid fiction best-sellers and Oprah book club picks unless they are recently released (in the past few months) or you can get them very cheaply.

In my next post, I'll tell you about some of the best books we've found while thrifting.