There are several ways to work them...It seems that they change the more time goes on and boxing gets more and more commercial...But here are 3 of the top ways

1. Flat fee EG. 1million win or lose...then stipulations are often added....EG promoter pays excess expenses and fighter pays his camp....or 1 million and fighter is guarenteed at least x amount of it...usually the champion is given such options

2.Sliding pay rate...I know sound weird....but here is how it works again it usually favors the champion or bigger draw...

opponent is guarenteed 1 mil...champion will take less but no less than 750,000 but get percent of gate or in todays world PPV buys if they exceed certin amount...sometime it can triple a purse

3.One fighter is guarenteed X the other Y...One takes X and gets to choose advantages EG ring size...gloves...again that usually favors the champ or popular fighter....

There is a lot more detail to go into but I am just giving the basic's


Purse bids and such are those details I won't get into because you could write for hours..things like that are usually for stuff like title shots and ranking and favor only the promoter in the long run