My personal rule: never agree to the door take, or any percentage thereof, unless you are willing to play for free. More often than not, the number of people who actually show isn't anywhere near what both sides expect, AND there is always, inevitably, and argument as to how many people came through the door. Even if you have your own guy counting, and the bar guy who check's ID's is taking the $$$, what do you do when you disagree on the number??? Fight with the people who run the bar, and never get to play there again???
So long as you ASSUME this is going to happen going in, AND are still willing to play if you get screwed, THEN go ahead and do it.