Tipping is a customer's gesture of appreciation for what they consider adequate, good or exceptional service. If the service was unacceptable they may choose no tip at all. People who work in the service industry depend on tips, it is their motivation to go above and beyond the call of duty. In every instance of visiting a provider, AMP or anything in between you know the basic fees up front, everything after that is a gratuity for you to choose, if you choose.
To me, it does not matter if the fee for service is 160 or 1600. If the provider clearly goes out of their way to ensure I am happy above and beyond the call of duty, I will tip, worthy of the extra effort they afforded me.
I'm not calling out anyone who disagrees. This is a forum of opinions and I just stated mine.