@DreekLass, That is so true, it is justified if they add a delivery fee for the service rendered. I know in the US I think you are still required to give tips to the delivery guy, but over here in my country you aren't require to give tips to them at all.
I know. I listen to a lot of American people on Youtube, or I am subscribed to them on Youtube, and many of them make videos about how much people should tip. One of them said that he ordered pizza recently, and the guy who delivered the pizza asked for the tip - said something like 'the tip goes in this box.' And the Youtube guy was not impressed by that. SO he did not tip him, and phoned the company, to where they gave him some money off on a next order.
I would never think of forgoing tipping - unless the service was really bad. However, even if the service was bad, I might consider ignoring the situation, guessing that it probably wouldn't happen again. Note, the justification for my attitude is the consideration of the fact that waiters and waitresses make most of their income from tips. In fact, in some places - it's nearly all of it.
Generous people are doing that and also those customers who are well-pleased and satisfied for the service rendered to them by the waiter. Let's not misconstrue of giving up as a means of getting a priority or a favor and also of spoiling the waiter for doing his routine work. Giving tip has a great impact on encouraging a better service for it is rewarding and nobody would deprive of giving more tips if they're indeed overwhelmed of the services. Besides I believe that it is more blessed to give than to receive as what the Bible says.