Serious answer, have him put the tickets on StubHub and buy them there.
The short story is, if the seller is trying to screw you StubHub will take care of you. One disclaimer: Skip to the last paragraph if you don't want my whole story.
Long story: I bought tickets to the Argentina/Honduras soccer game at Kyle Field on StubHub. StubHub had the seller transfer the tickets to them and then they transferred them to me via the 12th Man Foundation.
However, StubHub clearly never tried to actually access the tickets. They just received the 12th Man transfer link from the seller and passed it on to me, because when I tried to accept the tickets it turned out they were student tickets. 12th Man asked me for my student ID, which I don't have so I couldn't get the tickets.
I reached out to the seller, the 12th Man, and StubHub. The first two were dead ends. The seller swore the tickets were not student tickets and the 12th Man swore they were. That was fairly predictable, but Stubhub's reply said they guaranteed me some comparable tickets or my money back. They asked for a few days to work it out with the seller and then a few days later they sent me 4 different tickets in the same section. I was only trying to buy 3 originally. I have no idea if the original seller ever got the money, but I doubt it.
Of course, there's always a chance he could list the tickets and someone else could buy them before you do. I think who buys the tickets is out of the seller's hands once they're listed. You'd have to move fast, especially if he's giving you a good deal on them.