I left a $10 tip at a Chinese buffet I frequented in Finland to a friendly waiter. They insisted it covered payment for my next lunch. Finland doesn't have strong tipping culture, but it still felt strange for a restaurant to outright refuse a tip, especially a foreign one :D
Offering a tip can even be considered offensive. Something along the lines of "You normally do a very poor job, can I bribe you to at least try this time?"
Your point stands about tips being considered offensive, but isn't avoiding that rationale part of why tips almost always follow the service in question? I understood one possible reason being that people want their (hopefully diligent and appropriately generous) service to be seen as the default, rather than something worthy of an additional reward for any special treatment.
