I'll post this on FB with "I'll take it" but only if I'll actually buy the game at the advertised price without many concerns. I do that only because some folks privacy settings won't make it immediately clear that they have a message from a non-friend.
On here I agree it's mostly just folks trying to mark their territory, often too late even. Does it matter if you wrote pm sent an hour after the ad went up and 3 other people already messaged? Haha.