If a garage sale, why not a flea market? More horrifying, make it an indoor flea market like "The Dirt Mall" in Mall Rats. I can see that being a convenient venue for low end practioners and providers of icksome magic, as well as magical predators.
*Just had a vision of a desperate Nic with his unwelcome abundance of unhosted coins setting up a table, finding a host for a coin then wailing in horror as the new, prospective host walks over to one of those vending machines that mashes the coin flat while imprinting some kitschey phrase into it...*