To an extent this already happens. Barber shops charge more for women's haircuts, even though they're the same amount of work as men's. Health food stores charge more for anything labeled "Natural" or "Organic" although there's rarely any difference. Insurance for teenagers is sky high. Brokers charges fees to their clients based on their net worth, and lawyers refuse to take clients if they don't think they can, in good conscience, defend them.
As to the rest of your questions, the answer is always the same: lawsuits.
If you slight one customer or even worse a class of customers, you'd better be prepared in court to explain why or you will get fined, according to the laws Howard cites.
Private clubs, clubs serving only members who have paid something to join, are exempt from these laws and you have many who go this route in order to keep the blacks/gays/libruls out.