I will not pay for work before it is done.

If you have to worry about it that much then maybe this ain't the right shop. I'd gladly give Tony or Matt from my local body shops the $2k up front to paint my Dart if they really wanted it that bad. Small town, recommended by one of my best friends, etc....

It's best to start off on the right foot with the shop you plan to use. Trust is a 2-way street. I agree on the 1/2 now & 1/2 when complete as a good suggestion.