Yeah, you could see this outcome on the way.
Not sure how I feel about it or how to address it but the "taking a check" thing makes me queezy unless he signs somthing regarding the work and I don't think he will want to. Part of getting out of Clown College is to be a big a pain for as long as others will tolerate it.
Then again, you have the tractor inside and it will, I hope, stay there until satisfactory delivery. He's mostly whipped but likely will try one more if he thinks he can sneak it by you. Maybe jot him a letter regarding the financial and other details of the conversation and what is his financial responsibility. You could also send him the work order to sign and return.
It's slightly premature but good luck, my friend, and in celebration of this success I plan to crack open a bottle of three-week old Rolling Rock tonight. Visualize clinking glasses and a hearty "Salute!"