(said in snooty shrink voice) How does this make you feel?
Can you inspect all of the interior? (emp)
Your life will be riding on this work. If you feel comfortable, great. You might wanna think about what might happen if you sell the airplane. If it were me and I liked the work I would create a "proof of workmanship log" i.e. pictures, find samples of his primer process, research and find work to be shown to be in accordance with f.a.r. bla bla bla, vans print number bla bla bla etc. That woud help resale and piece of mind, but it could be quite a chore and be very very time comsuming. But you should get a lower price for the kit because of it. I realize interior pics might be hard since getting your hands on a $50,000.00 pro boroscope to take pics and video is going to be out of reach for most people. But you might be able to accomplish the same thing with small mirors and a flashlight and writing a statement in the logs. Basicly just verify the work and document it like you were an inspector signing the work off. Then you'll have your logs, piece of mind and resale. But it's an exprimental so do as you see fit, just my 2 cents.