Good:
use an escrow or another 3rd. party system. Or insist that you receive and move your money first.

Better:
Check up on the person you are considering doing business with.
What is their real name and home address? Tell them you want to talk on their home phone first. Couldn't find it? Then don't do the deal.

Best:
Never use PayPal. Even with the temptation of a high price.