I'd see if he'll let you come over, and see some of his work.
If he won't, say goodbye.
See what he'll offer you, and at what price, and go from there.
One caution I would give you is to not impulse buy.
I'd also be leary of anyone who demands money up front.
I'd be willing to pay for the actual parts going into the CP after seeing the cab at a decent stage of completion.
That will make it so that YOU have the receipt for the parts in your name.
I'd make him sign a delivery notice when I gave him the parts, that has a space for a second signing for delivery of the cab to you.
That way, if you do have to sue him for the money, he can't produce a fake receipt saying he gave them back.
If he tries that, you can counter with "why would I have signed THAT receipt instead of the 'got it back' part of my ORIGINAL receipt?".