Maybe he flew it to trim it out, sounds logical to me? As far as the build goes he can charge as much as he wants, this is America. Consumers set prices not retailers. Why did you not let the other shop do it for less, did you shop around? If the plane is put together correctly I would not sweat it. Now that I think about it all four of my planes the first tank of fuel was burned with someone else at the sticks, the only difference is I was there to watch nervously.

By the why I would highly recommend building your own planes whether an arf or kit. You will learn much about how and why the plane does what it does. The first arf I assembled was a Sig Kadet LT-40 and I learned things during that build I use every time I am at the field. This hobby is about "tinkering", might as well learn while putting together your first plane!