In most cases, yes they can accept what ever they want. Howeverr the Broker probably is set up so that the more it sells for the more he gets. Also in some states, now the seller only gets to deduct what the boat actually sells for, so he may not let it go. I guess one would need to know the agreement between, Donor and CHarity. Does the charity have clear and free title??
I would treat it just like any other, boat purchase. That being said, for 90K it better be a damn nice boat.