If it's not optional for rewarding exceptional service, then it should be part of the price. If everyone pays the same expected tip, there's no real benefit to

If it's not optional for rewarding exceptional service, then it should be part of the price. If everyone pays the same expected tip, there's no real benefit to having a separate line item on the bill. But practically, certain customers end up paying a larger share of the service worker's take home pay. Dynamic pricing based on customer's willingness/ability to pay is an interesting pricing model, but in this case the risk is entirely on the service worker who hopes enough people pay sufficient tips.