To tip or not to tip... Shakespeare is catchy, and now cliché. Oi.
You go to a restaurant. You are waited on. You are served. You are taken care of. You pay your hard earned cash to buy a decent meal. And after all that you come to the realization that for the service you received, tipping might or might not be a good idea.
Looking at this in the cynical way, the server knew he was going to earn less than minimum wage to begin with when he signed on for the job. He expects to be paid in tips to make up for this loss. But why should you tip? It was the server's own fault that he took a job with less pay. Again, cynical, but nobody wants to be expected to pay more than what they have already paid for the meal.
Sure, restaurants could operate differently. But they don't, so what should I, Joe Blow Christian, think about all this. Politicking aside, there is a sense in which we are called to love our neighbor despite what our neighbors intentions are. Our neighbor, the server, may intend to butter you up in order that you'll fork out the cash. Our neighbor, the restaurant, may intend you to fit the waiter's bill. You may be getting waylaid by the both of them, but that is no reason not to love your neighbor.
Instead of thinking this guy is stupid for taking such a low paying job and why should I help him (which, indeed, is breaking the seventh commandment), why should we not desire to help our neighbor? The fact is that sin prevents us from seeing this side of coin. All we can see is how we are getting ripped off. (Again, breaking another commandment by making ourselves the most important person.) St. Paul writes to Timothy (1 Tim. 6:10) "For the love of money is the root of all kinds of evils". This just goes to show how money can put enmity between us and our neighbor in something as simple as tipping.
However, take comfort in the fact that Jesus Christ has taken our sins against our neighbor upon himself when we do sin against them. And that he has given us his righteousness in return that we might not be condemned forever to an eternity of hell. We also pray that the Holy Spirit would work in us to produce to good fruits of faith that we might always help and serve our neighbor.
Now, I am not saying that when you don't tip it is a sin, but just remember that when you greet your neighbor wherever that may be, that person is your neighbor, so love him.