Art Williams once quoted "All you can do is all you can do and all you can do is enough." The customer is not always right and part of what we do is educate our customers to the reality of the market place.
Minimum service is doing what you say you will do and integrity is never promising something you have no control over. The most important thing we have no control over is the market place. There are basicly two types of property owners selling property. One is the owner who will sell if they recieve enough money. They are under no pressure to sell. The other is the property owner that needs to sell for whatever reason, personal,financial,relocating etc. The worst circumstance for a real estate professional is a property owner that needs to sell but takes the position they will sell if they get enough money. That is a situation that you can not win.
I believe there is no such thing as an over priced listing just over priced circumstances. Most problems between real estate professionals and customers evolve from misunderstood circumstances. Deal with those circumstances up front and honestly and you won't want to fire as many customers or clients and they will not want to fire you.