This is most likely a scam. I contacted the buyer via email, offered to send half of the coins for half of the payment, then the other half of the coins for the other half of the payment.
What I find interesting is that with so many ways to use a PayPal scam (chargebacks, disputes, other people's accounts, etc), this user has chosen the most simple and obvious method.
You have to pay first. If not, I'm not doing it your way.
Leaving negative trust, because I frankly don't trust them.