Oh, ok, forgot about that, you got me...But that happens already anyway, players set each buff for 1 FSP (plus the gold offer for normal buyers), the guildmates buy from the FSPs to not overflow the seller wallet with delicious gold, and when the seller comes back he send the payments back to the guildmates.
But sincerely that's not very important because most of the players have access to all the buffs (by self buffing or guild chat) anyway, if someone is willing to run auto-refresh 24/7 just to give free buffs for guildmates, let it be, I'll not really be much bothered, but I think the idea of a guild buff bank a very different history.