Ye ole Replica Builder say "Replica like watermelon. You done kno wat you got til you see wat inside". And to that, I say, talk to someone who has purchased a car from the builder that you chose and see how satisfied he is with the car. Ask him questions about the finish, operation of all of the options, details of the fine points, (such as the ride and handling, trim gaps, tire spacing, not just a picture) and what does the chassis look like under the skin. If you feel that you are not qualified to tell a good weld from a bad weld, then take someone with you that does. The car will have to be raised on a hoist for this. NEVER, NEVER, (DID I SAY NEVER) PAY UPFRONT and trust the builder to deliver whenever. I would bargain to a 1/3, 1/3, and 1/3 at delivery after inspection.
Jim