Consider putting the money in escrow with a banker or CPA. You can get someone in your town to be your agent and contact a person in his town who will act as his agent for a small fee. Your agents can draft up a simple agreement accpetable to both parties that will cover the "You do this, and I will do that," to avoid the "he said, she said" stuff.
The agreement can specify how much of the escrow fund will be distributed by his agent before the work is done (pays for show up, loading, gas, food etc. on the road). Then when you get your truck and you are satisfied, you tell your agent (in writing) to release the remainder of the escrow fund to his agent and he gets his final payment.
This stuff can get real messy across State lines if anything goes haywire--questions of venue, standing, etc. which you can clarify ahead of time with a simple contractural agreement administered by a disinterested third party or parties.
You can probably get a draft contract somewhere on the internet that will cover your State, and be acceptable in his State as well.
OK, so I'm a fuddy-duddy. A few bucks for a fuddy-duddy now can be a lot less costly and keep everybody happy later on.
