Smile: This speaks to your openness as a service person, your approachability. The phrase "the customer is always right" is a well-known rephrasing of this. Customers naturally seek out places where they won't be belittled or brushed off, even for unusual requests.
In wholesale trade, mention that you could have a certain perk available; perhaps, a quantity discount for them as a regular customer. For example, paper companies often give printing companies who are regular customers the next price bracket so that a ream/package of paper or a box of 500 envelopes is priced at the carton price and a carton is at the skid quantity price, with free delivery on a certain day, like on Tuesdays, to their part of the city or out to a local town--and offer free delivery on a certain large quantities on other days, which may encourage the customer to stock up.