Well I don't treat dogs differently depending on if the owners tip. Guess I can't speak for everyone though.

I don't expect tips unless I've gone out of my way to do something (for example take all day long and brush out a really matted dog because they begged me not to shave them). They are appreciated but not expected. The ones I get are few and far between so if I was expecting a tip on every dog I'd get disappointed an awful lot lol. I'll take a really nice owner and great dog over a difficult dog with a $10 tip any day.