Single post in External links / Marketboard change

Regarding to seeing who bought what at Marketboard is okay, no complaints about that, my only worry is and how should we deal with, for example, I have bought an item that's way cheaper than typical price for the item, as the Seller has missed one 0 in price. The Seller only notices they've made a mistake only after it's been sold, so they can go check who bought it for that price and asking/demanding the Buyer to pay the rest or return the item. I know I'm talking about a hypotetical situation and it's very unlikely to happen, but in case somebody does message you, regardless of their tone in message, how should we proceed with that? I know it'd be a nice gesture to help out the seller, but I also don't want to be messaged about something that I couldn't have been messaged about until now. I've made mistake of selling items for cheaper without realizing because of typo but even if I did have the chance to, I wouldn't go bother the user about it just because Marketplace is supposed to be final, this isn't something that's been agreed upon like at trading threads.