Need helps urgently Paypal Payment

Hello everyone
First of all, sorry if this is not a right place to post this thread. I am new to this site. I have one question, I want to sell dota 2 keys for real money through paypal. The person has already sent me the money via Paypal but when I checked his profile, he was banned for charge back money. How do I avoid this situation. The amount of money he sent is still in my Paypal account. How do I refund to the person? After I sent him the thread that he was banned for charging back the money, he unfriend me so I do not know how to return him. On top of that can someone tell he how to prevent money charge back.

Thanks alot

Sorry this is the thread that ban the person
http://forums.steamrep.com/threads/megan-fox-76561198109399790.49551/

1. Moved to the General section, more appropriate.
2. To refund, you can click on the recieved money and select to "refund" the money.

Or he'll charge back.... better to refund to get rid of the issue, and avoid issues with Paypal's investigations etc.

"On top of that can someone tell he how to prevent money charge back."
Can never stop this. You could find someone with a lot of rep on sourcerep and a long trade history.
Unless if the trader decides to go evil one day, odds are he won't want a scammer tag.