Most mattress stores offer to dispose of your old mattress for free when they deliver the new one--but throwing away even a very old, used mattress is throwing money away. You can quickly make some extra cash by selling your mattress online or through a garage sale. Here's how to sell a used mattress.
Price it right. Even if you paid thousands for your mattress, you're probably not going to get more than a hundred or so if it's used. If it's free of stains, a designer brand and not at all lumpy or moldy, price it on the high end, while mattresses that seem very used and worn should have a modest price tag. Remember, your plan was to throw it away so any cash is better than no cash.
Try selling it on Craigslist. Upload a picture if you can brag about its pristine condition and be sure to note if it's a high-end brand or if you've gone to any extra lengths to make it marketable, like getting it professionally disinfected. Require local pick up only and accept cash or Paypal, no checks, to avoid Craigslist scams.
Post signs advertising the used mattress in common areas of your apartment building, community billboards and coffee shops that allow for sale signs. Play up the mattress's comfort and great condition if you can brag about those features and list a price you can use as a starting point in your negotiations.
Sell your used mattress during garage or yard sales if you can't get rid of it using Craigslist or through billboard postings. Expect to get considerably less money at a garage sale than you would online.