First off, I would not buy a completed car. Personally, all the pleasure is in the building for me. Once the car is complete or near complete, I'm ready to sell it and buy another project.
Secondly, I would not buy a car that I could not personally inspect and drive. I have always, ALWAYS, ALWAYS been disappointed with other people's work.
Thirdly, I would not buy a competed custom car that has not been appraised by a professional appraiser.
I'm pretty sure that I have not helped you here, but at least you have my take on it, for what it's worth.