i always goes between 15 and 20%, or 1$ per drink if i'm in a bar.
i was barmaid a few years ago, and the way it work in quebec (and probably in other province too, but i honestly dont know if it's the case), you get paid minimum wage for worker with tips (which is usually 2.5$ less poer hour than regular minimum wage). and you get your tip, minus 5% that we gave to buss boys and hosts. then, at the end of the year, you have to do your taxes. But what you must declare in taxes is not just your base pay. You must add 8% of your sales in tip revenu. and you pay your taxes based on that revenu.
So when people dont tip you, you actually lost money...