Insist upon a written and dated statement of the item. Finally, never send cash. Personal checks are usually held until they clear, while money orders and cashier's checks are honored more quickly. Paying by credit card offers some protection. These ideas are mostly for buyers.
Sellers also have to be careful about what they are doing.
In 1994, they worked at Microsoft. Today, you're nobody unless you shop on eBay. Note that the prices of items are included in both groups. If you know what you're doing, you can get some real bargains. Some of you may have noticed or suspected that I, too, have become addicted to on-line auctions.