All of that sounds good to me except paying cash for something and not taking it with you when you depart

That will mean that you have to trust him to not take off certain parts, switch things etc prior to you getting it. If he has your money and you have pictures…doesn’t necessarily mean you will get what you paid for.
For example if I paid for a car in the manner in which your going to do… (I can talk cars better than combines) it might be working with new spark plugs and wires and decent rotors designed to give me a good impression etc. When it arrives to me, the rotors could be changed, a few spark plugs could be missing causing the occasional misfire etc… Not things that I could readily or even consider photographing but are definitely different than when I left the vehicle after paying for it. Bottom line, I am trying to describe bait and switch which might not be apparent in photos but done between sale and possession. Guard against that type of stuff please.