How can you safely trade something with someone online?

Question

Like, through the mail. How can you insure that both people must send the items. On eBay, PayPal is used to insure payment. It's the same thing, on sending through the mail. Thanks.

Answer 1

You can't.  Its buyer beware!

Answer 2

By using an intermediary like EBay, where both people put up their items.