But what if someone wants to pay way too much for something I provide?
This is how collector car auctions work. Let's say I put my Ferrari up for $125,000 reserve, but two guys get into a bidding war and the winner ends up paying $165,000.
I get $40,000 over my minimum selling price - and I don't see that this is unethical. It was worth the $165,000 to the guy that bid it - at least at that moment in time (what with all the hospitality champagne).
The only way I would be unethical is if I did not give him a clean title, or misrepresented the car. Like maybe selling him a Corvette with an aftermarket fiberglass body (if he were that drunk).