The short answer is, when you can draw a crowd, you can draw a paycheck. The longer answer is that bars and other venues that book live music are counting on the act to bring in a thirsty crowd. They make their money on bar and food sales, not on ticket sales. So the right time for you to start demanding to be paid is the moment you prove you can bring people in the front door ― and not drive them out again! If you are an unknown entity and it's not guaranteed that tons of people will come see you, the venue owner might start off offering you a share of door sales rather than a guarantee. That's pretty standard. Just make sure to agree that he or she can't dip into the door sales to pay for the bartender or the bouncer. That's not standard. Everything else directly related to putting on the show, like who pays for the backline and sound mixer, for example, is a matter of negotiation and should be sorted out before the show.
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