He can do chargeback.

Yes, very possible. You can get your money back up to a certain amount of days, depending on local laws. It says it right after you send it. Mine for example states that my state allows up to 120 days.

I would have the person buy keys, from someone else, with their money. That way, you can get the same amount and if they are scamming, at least it isn't you that pays the price. Let the key seller decide for themselves.

People ask me all the time if I will trade for Paypal, but I rarely accept it. I have to really want the deal or believe that the person is legit, before I am willing to take it.

Bookmark this reddit thread!(scroll to middle of the thread for chargebacks)

https://www.reddit.com/r/Steam/wiki/scamtypes

Chargebacks are a worry, so for PayPal trades, I require the other user have SteamTrades reputation going back at least 6 months, and often a minimum of 50 trades with different users.

With digital media, PayPal will practically always allow the refund. If you can't live with the loss, then don't do it.

I'm afraid this thread would make scammers aware of this evil scamming method more...