If you can't trust the owner/builder, I don't know who you can trust.
There are a million things that can kill you when flying, regardless of if the aircraft is experimental or certified. About 999,930 of those things we aren't even able to see when preflighting.
Basically, as pilots, we're putting a lot of faith in things outside of our control every time we take to the skies. We're trusting every pilot who flew the plane before us, as well as every mechanic who worked on the plane over the years. You and I both know there are plenty of events which could have taken the plane outside of its design envelope at some point in history, but we fly it anyway.
I don't see anything naive about trusting a guy who probably knows more about his plane than any A&P or test pilot ever will. Get too paranoid and a person will stay on the ground all the time.
Now, all of this being said, if a person still isn't comfortable giving the flight review for some reason, by all means, don't do it. I just object to the notion that the owner isn't a safe source of information about the aircraft. All of the owners/builders I've met have been extremely knowledgeable and safe with their aircraft.