Go to the shop and tell him that YOU want to test drive it or something, then don't take it back to the shop. The tranny's already toast. Bottom line is he has your car. That is by far the biggest risk. You HAVE to get your car back. Once you have your car back, then work on getting your money.
Better to have your car and be out $600 then to be without your car AND $600.
Better to have your car and be out $600 then to be without your car AND $600.