Dunno if this idea has been put out or not, a bit lazy/irritated this morning to look.
Overbidding. Paying 2x 3x even 20x the price of something because you're tired or distracted. Then the seller won't return the extra Gil, even if you return the item. How many of you have been there?
Well the AH shows previous prices, average them up, then if you bid 2x or higher than that, a popup will appear for confirmation. Telling you that you were bidding 2.5 or even 12.8 times the average prices of <item>, do you wish to continue the purchase.
I don't think it would take too much coding to impliment.
And people like me won't pay 520k for a 25k helm by mistake again.