I hear from car friends and acquaintances being offered over market for collector cars at a Cruise-In or even at a stoplight.

These are tactics to "open the conversation" of selling a car that is not for sale. Typically they negotiate backwards after the car owner opened the idea of selling and can look at the car up close.

I think this guy is trying to do something similar. Once he got his deposit in, he totally changed attitudes and ramped up the pressure to close the deal. He is just choosing to work his way backwards AFTER he paid and took possession.