There is always a chance that someone is unscrupulous and will cheat, however I have made several purchases on AH and have never had a problem- quite the opposite- the sellers that I have had contact with were very honest and straight-forward.  As a safe guard one thing that can be done is look at the sellers history.  but the cheating can go both ways.  My preference is to pay for something with a personal check, made out to the seller.  The seller will need to endorse it and the check will return to my bank.  So I have a record of the sale.  These purchases are made with the understanding that the seller will not ship the item until the funds from the check have cleared- which anymore, thanks to computerized banking is generally in a day or so; however I have no problem with the seller waiting a week or 10 days to ship, but most want to get the item gone, so is sooner.