Again. That some proceeds are going to charity will provide the necessary cover a lot of buyers will want to simply spend whatever it takes without looking like a fool who overpaid. "It is after all, darling, all for a good cause!".
I promise you they will also try and take the tax deduction.
Plus I would imagine the tax attorneys who have the kind of experience to go up against the government on something like this are quite expensive.
Buyers can deduct the amount paid above "fair market value" for items purchased at a charity auction. But For an item like this, there is no way to determine fair market value. Similar examples trade in the $120k-$180k range, but they weren't owned by Paul Newman.
Expensive but effective. And it's more expensive for the IRS to fight it, and they are already under enormous pressure.
I think an agreement is negotiated quickly and quietly so that all parties feel satisfied. But at the end of the day, if you're bidding on this watch you are not sweating it that much either way.