Created for the merchant Ghaskari the Greedy, who sought to make a gift of it to his rival, this elaborately-embroidered and bejeweled coin purse imbues coins withdrawn from it with a deficiency in satisfaction. When a player spends money taken from this purse, a payee who would normally be satisfied by the amount decides that anywhere between 25% to 50% more is required (whatever math is easier in the moment).
The purse's effects go the other way, too: items sold by its owner renders 25% to 50% less than its expected street value.
The purse is inlaid with 1d12 precious gems, themselves worth 50gp each. If these gems are removed, the purse's potency doubles. If they are sold, its owner mysteriously misplaces 1d8 GP per day.
Abandoning the purse frees its now former owner from its effects, but destroying it makes the base curse (25% to 50% devaluation on all vendor interactions) permanent.
To destroy the curse, the spirit of Ghaskari the Greedy must be summoned and defeated in a bidding war for the purse. The player will likely be eager to get rid of the purse, but if Ghaskari wins the purse, then he curses the player with permanent devaluation on all vendor interactions.
Ghaskari is fierce when bidding but ultimately is a consummate cheapskate. If the player bids 10 times the value of the purse (based on the gems and what ever coins are in it at the time), Ghaskari becomes angry and destroys the purse, thus nullifying the curse for this and all players affected by it.