Quote Originally Posted by lance Uppercut
Purse bids only occur if the fighters cannot work out an aggreement themselves. The percentages in the purse bid is determined by the alphabet group that demanded the fight.
Exactly. Any promoter can put in a bid for any fight, but usually it is just the two promoters of each fighter.
On the day the bids are due, each bid is opened and the highest bid wins the fight.

Depending on the santioning body the final bid is split between the 2 fighters. Most champions fighting a mandatory challanger get a 75/25 split.