I was looking through upcoming amateur venues within 150 miles and come across a promoter stating that if you want to fight on the card you "must be able to sell 30 tickets to the event". I'm looking into fighting for the first time and wondered if this is typical for an all amateur event? 
Pretty typical from what I have seen.
Does a few things IMO
1. Fighters get practice promoting themselves
2. Fighters build a following
3. Promoter gets gaurenteed ticket sales
etc...
I've seen people argue that it is a shitty practice.
They didn't do that when I fought, if I would of had to I would of said no, I had other things to worry about. 
That's sketchy bro. Find another promotion.
Not in Chicago. You're given tickets and encouraged to sell them to your Friends and Family who would/should want to see you fight, but, it isn't mandatory in any way.
We dont do that her in OK, sounds sketchy to me to.
The minimum tickets sounds strange, but promoting is a business, and being a fighter is a business. So both should want to sell tickets to make the event a success.
Fighters should want as many people chearing for them in the crowd as possible. It is no fun to have no one to support you.