it's not what I'd consider an unreasonable request.
I have used aerospace reports in OKC, they charged us about 600 or 700 to escrow and handle the closing on our plane, my experience was top notch. Basically you call and give them the plane and seller info, you wire them the funds, the seller sends them a bill of sale. Once you're good to close you call and authorize the closing, then they wire the funds back out to the seller and record the sale with the FAA. They also handle the title search and such. They would also hold the deposit, not that there would be one in this case.
If it's a good plane and what you want I would consider it to be a minor speed bump in the process. In fact I would let aerospace reports handle any closing I did. They offer a 10% AOPA discount, too
If you're buying the plane to build hours and sell perhaps you don't care about a super thorough prebuy. If they'll entertain it I would consider the shop in willmar MN, it puts the plane that much closer to you and they were very reasonable on a prebuy they did for us (we didn't purchase because of it). I doubt they'll go that far, he doesn't sound terribly serious about selling.
If you're financing IIRC our lender closed the loan and sent the funds ahead of the airplane closing so that was all super easy.