Selling stuff online can be a great way to make some extra cash. Craigslist, Facebook Marketplace, and other sites attract many buyers — and scammers.

A common scam is the fake check overpayment scam. The scammer offers to give you a check for more than the selling price. They tell you to deposit the check and send the difference back to them.

The check is fake, but if you deposit it, it’ll appear in your account balance. That’s because banks must make your money available quickly, usually within two days.

When a bank says the check cleared, that doesn’t mean it was a good check. It can take weeks for the bank to figure out the check was fake. By then, the scammer has the item you sold and the money you sent back. And the bank takes the money from the fake check out of your account.