This is a fascinating topic and I agree with you: in customer facing roles it is necessary to handle these situations. Customers are not "always right", but business rules (and common sense) suggest it's appropriate to take the higher ground and give them some leeway, if nothing else for a matter of opportunity. Business is nothing personal and a rude customer should never bruise anybody's ego, while the effort spent to handle it will usually pay back.

It goes without saying that a customer expressing direct threat or, worse, getting physical, is not acceptable and shall be handled more appropriately by security personnel.