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A little thin in the wallet lately? Retailers will pay for your unwanted books, compact discs, DVDs, and old and broken iPhones -- without requiring you to purchase new ones.

Unlike government-run programs or in-store promotions, most of these services operate exclusively online. Consumers are required to mail in their items and then wait to be paid by check or PayPal. The draw is the convenience. For example, rather than lug your books to a used-book store, you can take them to the nearest post office or FedEx drop-off location. And with most services, shipping charges are paid by the retailer.

Of course, any business transaction conducted through the mail and on good faith comes with risks. You might be quoted a certain price for your stuff, but if the business deems your description inaccurate, that quote could change. Or the business might reject your items altogether and discard them unless you cover the return-shipping costs. And because these are all for-profit ventures that resell your items and pay the shipping costs, they are likely to offer you a lower price than you might get if you dealt directly with a buyer on eBay or Craigslist.

Still, if you're looking for an easy way to clean out your bookshelves or entertainment center, these services might be worth a try. Just be sure to vet a company before putting your stuff in the mail. Check its Better Business Bureau rating. Anything lower than an A or B should raise a flag, says Michael Galvin, a spokesman for the BBB of Southeast Florida and the Caribbean.

If you see a lower grade, call the local BBB to find out why. The branch can tell you whether there's a pattern of complaints about the business and point out other concerns. If there are registered complaints, check whether they have been resolved.

And before you send in your stuff, get an idea of what it's worth and how that value compares with the company's quote. The easiest way to do that is to check the selling prices of similar items on eBay, says Doug Norwine of Heritage Auction Galleries in Dallas.

Here are three businesses to consider:

1. Books

Run by McKenzie Books in Beaverton, Ore., Cash4Books.net specializes in college textbooks and technical books, which are more likely to pay top dollar than, say, paperback novels. How much you get depends on a book's weight and retail value, how quickly it is expected to sell and how many copies are already in the company's warehouse.

On average, sellers get about $20 per book, according to the company, though a check by SmartMoney yielded lower results. The personal finance and investing books we ran through the Cash4Books.net system would fetch about $5 at best (we were quoted $4.50 for "The Progressive Discipline Handbook: Smart Strategies for Coaching Employees," with CD-ROM, by Margie Mader-Clark and Lisa Guerin). Getting an online quote is easy. Just enter the book's ISBN (international standard book number).

The perks: Shipping is paid by Cash4Books. You can get paid by check or PayPal.

The fine print: Cash4Books will not accept books with tears to the cover or pages, major wear to the binding, missing or loose pages, water or other damage, or a strong odor. If any books are not accepted, McKenzie will ship them back only at your expense.

Due diligence: The Better Business Bureau registered 14 consumer complaints about McKenzie over three years. All were resolved. The company has an A+ rating.

2. CDs, DVDs and games

Do you have old CDs, DVDs and games gathering dust on your shelves? A Santa Barbara, Calif.-area company, Morninglory Online, which runs CashforCDs.com, might buy them from you. How much you get depends on a disc's title and condition.

We were quoted $20 for two CDs, one DVD and three games (one each for PlayStation 2, Wii and Xbox), each in good or excellent condition. But we did strike out on the six other CDs we inquired about, which included INXS' 1990 album "X" and Pearl Jam's "Ten" from 1991.

CashforCDs.com wasn't currently buying those titles. The company said there is an oversupply of certain CDs, with not much demand, a trend that isn't likely to reverse.

The perks: You don't need the cases -- just the discs and the front and back covers.

The fine print: For copyright purposes, the company requires the front and back covers of each CD, DVD or game.

Due diligence: Morninglory Online is rated A+ by the Better Business Bureau and has had no complaints filed against it during the past three years.

3. iPhones, Zunes and other small electronics

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Don't just toss your old or broken iPad, Zune or iPhone. Rapid Repair of Portage, Mich., will be happy to pay you for it. The company, which has been in business since 2004, specializes in repairing small electronics but also buys them from consumers to use for spare parts or to repair and resell as refurbished. How much you get for your unwanted gadget depends on its model and condition.

The perks: You can get cash for an item that you can't otherwise sell or repair.

The fine print: Rapid Repair does not accept gadgets with liquid damage -- a diagnosis few users can make on their own -- so you might end up sending in an iPod and getting nothing in return. Postage is paid by the seller, though given the size of the items, the cost is fairly low.

Due diligence: The company has an A rating with the BBB. All seven complaints filed against it in a recent 36-month stretch were resolved.