It varies wildly man. My company Music People, run clubs around Sydney and put on bigger events, as such we have a partnership with future entertainment and all our djs, promoters etc have to sell future music tickets so that we are able to host stages at the festival, get big artists for official after parties and even our djs get sets at future because of this partnership. Tickets for actual events you are playing at, often you will be booked and asked if you can help sell some tickets. So long as there is no quota i don't have a problem with this, because until you have a big enough name to draw a crowd you should be bringing friends to support you to gigs. There are arsehole promoters out there who will make potential djs sell a certain amount of tickets to get a gig, it's then no coincidence these events have shit djs, as they book them on ability to sell not dj. I stand by my comment on facebook tonight, Promoters bring people to the club, djs keep them there.