Here is how I trade safely with paypal.
Have them VIDEO RECORD them logging into their paypal and showing that it is Bank funded and has NO CREDIT CARD ON IT! Look at the email address in their paypal home as it is clearly evident and mark it down.
When they send you the money MAKE SURE it is from the EXACT address you saw earlier, some people will change even just one letter to fuck you up so watch out.
Claim and cancel is shown on your paypal, it tells you when a buyer has filed a claim against you and it tells you when they have dropped the dispute you simply need to pay attention.
If they don't want to record it (many people refuse to), then have them take screenshots if you pay attention it's pretty easy to tell if someone has edited a screenie (you can find programs which can detect displaced pixels.)
Thats the only way i would ever take paypal. And remember that they can still call paypal and say they didn't do the transaction. So watch out.