More and more establishments are installing British-style cask conditioning facilities, and this can lead to problems for you as well as the bar owner. He or she should train workers to manage such natural fresh-conditioned beers. They should be receptive to constructive criticism from patrons.
The price of beer and the size of the serving are also important. I have found pubs that, I suspect, use the 14-ounce glass as a pint measure. This is inexcusable. If you suspect your local is pulling that on you, go with a friend (don’t do this alone) and bring a measuring glass to determine the real measure. If you find something like that, you should raise hell in a fairly loud manner, so other customers will be aware, too. Of course, not all bar owners will receive such criticism graciously, and the two of you should be prepared to evacuate those premises on short notice. Prosit!