Tone is the actual product here
A return is the one conversation where the customer arrives unhappy. The paperwork can be instant, but the reply cannot sound like paperwork. You set the tone in your own words, warm or formal, and it holds that even when the customer is sharp with it. It apologises once rather than three times, it does not repeat itself, and it never implies the customer is at fault. That is the difference between a return that keeps the customer and one that ends the relationship.