I'd go ahead with it. As long as the car is fine and you have the paperwork/etc in front of you, what is there to be worried about? It's not like you're not checking it out before you buy it as with any car purchase. Worst case if anything does come up fishy, which I doubt given you said he has an internet trail of successful car sales, why be concerned?

I think he was dodging signing over the title because I think a person can only do X title transfers per year before they need a dealers license. He works at a dealership, but doesn't necessarily have a dealer's license.