The most famous and successful fashion retailer in England coined the phrase "the customer is always right" - this is a philosophy you may learn well to apply.
Rule 1 - always listen carefully to a customer and always presume the customer knows best
Rule 2- always repeat back to the customer any request the customer has made to make absolutely certain you understood the customer's request
Rule 3 - only make your own suggestions / recommendations when the customer specifically asks or when it become obvious the customer has screwed up
Curious to know who that was?
I endorse your rules.