I choose to believe the deal was straight up, at this point until shown otherwise. Not enough evidence for me to conclude it was a "shill" bid or worse. Maybe,,,,,, maybe not!
Wether he did or didn't have someone offering $25K is irrelevant to me. A classic (and moral, correct and legal) tactic to try and get a higher dollar for your sale.
"Well, I'll let the car go for $20K, but my neighbors brothers mailmans sister offered $25K. And I'm SURE there are others just waiting to bid more. But for you, my friend, maybe less."
Classic used car salesman if you ask me, no foul, I EXPECT that! Buyer beware, be suspicious, it's all part of the sales game. Someone got a nice car for $20K,,,,,, (or, did they)?
