Reading Arts (UK)charge the service charge even if you pay cash at the box office. I order mine online so they have to pay the postage out of the service charge as there is no difference, also saves me queueing on the night, especially if my train's late. It is usually better to go direct to venue box office online rather than third party websites in the UK. Theatres have started adding extras for "heritage restoraton costs", giftaid etc. We've found if you turn up at a theatre box office with proof of age (ie over 60) and want matinee tickets you can sometimes get great discounts. We saw popular Porgy & Bess for £20 each when cheapest advertised seats were £60 each.
One of my pet gripes with local venues that advertise membership with money off entry to find a)door staff have never seen membership card before and haven't been trained to offer discount and b) discount never seems to apply for some reason.

RtS