When it doubt, wait it out. Scammers typically will just reverse their payment if they do not receive their domains within a few hours without asking you about it, unlike true buyers (who will likely contact you first to see what's going on). Also, if the user is a NamePros member make sure they have good feedback, and never deal with a '0 post' user. They have scam written all over them.
EDIT: If you are simply too worried just refund the money. According to that 'hi5 profile' in the post above the guy is from Romania. Be wary, because a large number of domain scammers are from foreign countries where the laws are different.
