Tipping is fine, tipping culture should be exterminated. If you want to give a gift to someone who has gone above and beyond what you could reasonably demand of them, as long as it's not a bribe to neglect their obligations to someone else, good for you. But I would never use any service whose provider expected a tip, because under-quoting your price and slapping a 20% hidden fee on top is by definition not good service.