If you aren't talking about currency, "buying soles" usually refers to one of two things:

: Peruvian banks and exchange houses are notoriously strict about the physical condition of your foreign bills. They must be in pristine condition —no tears, ink marks, or heavy folds—or they may be rejected.

: You can find exchange booths (Casas de Cambio) in almost every Peruvian city, typically centered around the Plaza de Armas (main square).