In some states it is actually illegal for bartenders to give away free drinks... I'm just saying, liquor laws vary, but bartenders do it for good regulars. The main question is how much did you tip and how much did beers cost. If beers cost $3 and you had tipped $10 for the night (beer and food), you don't deserve a free one, but if you had tipped say $15, I would probably slide you a beer.