Back in the late 80s we started off playing the Kings Head in Fulham. The deal there was we had to get 15 people in after which we'd get 1/3 of the door take... If we didn't get that many we'd have to cover PA costs of £25.
Luckily we managed it every time we played there, sometimes only just!
But that was the only place we played that had that sort of deal. Later, we played all the Mean Fiddler venues and the Rock Garden quite a few times and never had to pay, though we didn't make much...