Sites like eBay and Craigslist offer a huge variety of items and services. The sites are also the perfect place to run a scam. Most notably are counterfeit check scams.

"They get a response via email by someone that says they are very interested in purchasing the item. This is our suspect. They told them they are going to send them a check. They're going to get a check in the mail," said US Postal Inspector Kim Gordon explaining how the scam works.

When the seller receives the check it is for more than the price of the item being purchased; sometimes hundreds of dollars more.

Gordon explained, "The suspect calls them again and says, 'I sent you hundreds of dollars more. I really need that money to go somewhere else. Would you please deposit the money in your bank account?'"

Then, victims are asked to wire the extra money to an address.

"They find out later from the bank that it was a bad check. It has bounced because it was a counterfeit check. And they are on the hook for all of that money," warned Gordon.

Postal inspectors say consumers need to proceed with caution when using auction sites.

"There is a very large warning that appears on Craigslist that the minute you submit ad placement," said Gordon. "The word warning is there and it says be weary of foreign responders to your ad."

Postal inspectors say it is important to remember there is no reason for anyone to send extra money for an item.  It is a sure sign you might be the target of a scam.