My 2 cents is it sounds like you have had many conversations to confirm that he is not running a simple scam and deal appears legit. I would say that it seems reasonable to me to have 5K down and the rest paid before the machines leave the truck. (if you were shipping via freight company I would say all cash up front) Couple reasons:

1. You are delivering the games yourself so not any risk of delivery scamming and you never seeing them again

2. He is putting a lot of trust in you for a deal of this magnitude also. Easy to look at it from your point of view but he likely has concerns that you will not deliver the games to him and paying when he sees them does seem fair.

3. I have no idea how many buyers are out there for complete collections like this. If it is rare I would say go for it, if they are common maybe not worth driving across the country.