It's not really a question of being mean. I'm sure most of us here like to help out newbies, and the OP has certainly done more on his part than he is obliged to.
He's been helping this guy out for three weeks, have to cut the cord somewhere. You can't provide lifetime support for everything you sell. lol
More to the point is ... I like to help out people who are polite and that are enjoyable to talk to, as do most people I assume. The buyer does not seem like one of those. I'm sure this whole thing wouldn't be a problem if he just tried not being such a tool?
Anyway, to the OP, just cut the cord bro. Tell him it's a new kit, you've helped him out enough and point him to the nearest LHS or whatever. Be nice but firm.