What banks will change dollars into pesos without requiring you to have an account with them?

Banco Piano, Microcentro, Caballito, and Flores will exchange dollars for pesos with no hassle. HOWEVER, the green must be pristine! Not a mark, no a blemish, not stampings, nada. Pure as if it just left the mint, or they will discount the bill(s) in question 20%! (I have found many banks do the same)