Service is not like sales at all. I'm an electrical engineer, I deal with salespeople ("business development managers") from my employer's suppliers every day. They are professionals, selling complex products to other professionals for substantial salaries + commission. I assure you that people do not flirt while describing the properties of the $1 million STATCOM they are selling.
In most manufacturing or construction industries, salespeople send gifts (on their employer's dollar, not their own) to their regular customers, not the other way around. And that's a professional courtesy, not a way to make a living. I'm talking about sending a box of chocolates to the purchasing manager who does seven figures of business with you annually.
In many restaurants (i.e. family restaurants, chains) the server will absolutely not flirt with you. However, in many restaurants that is part of the expected atmosphere. It is even possible to get a steak at a strip club. Someone has a want and someone else chooses to provide the service. This is the free market.
Almost every restaurant/service runs a "comp tab", servers/bartenders/managers expect to give away a certain amount of goods to regulars and other good customers. Many sales jobs are 100% commission, which is priced into the sale. Tipping just exposes that commission to the customer. In any sale, sometimes commission has to be sacrificed for a difficult customer. The service industry is no different.
In most manufacturing or construction industries, salespeople send gifts (on their employer's dollar, not their own) to their regular customers, not the other way around. And that's a professional courtesy, not a way to make a living. I'm talking about sending a box of chocolates to the purchasing manager who does seven figures of business with you annually.