A nearby pet store used to have people who insisted their snakes would only eat rats/mice of a specific gender, color, or even pattern. They solved this by instituting two different prices. The store charged their regular price of $X/rodent for the employee to select the feeder of appropriate size. They charged $15/rodent for the customer to select a specific rodent. Almost overnight all of these people discovered their snakes were suddenly neither murine sexist nor racist in their appetites.