In Princes of Florence, the bugbear is this rule:
A player may move his figure backwards on the fame track at any time during the game. For each space moved backward, the player takes 100 Florin from the bank. (p.10)
What I've seen (and experienced...) a few times is a player sacrificing their chances of victory by spending ludicrous numbers of prestige points to deny other players auctions in the late game.
Basically, I'm trying to find a house rule that will prevent this "taking you with me" behavior.