As the others have said, it really does depend on the arrangement between owners. I think that once you do sit down and discuss the 'deal,' it would probably be best to make a paper contract that you both sign so it can be tracked.
Ordinarily I would say that with a female of the same value of the male to be borrowed, and the caretaking of the eggs and gravid female done mainly by its owner, the owner of the female should get....
-First and third choice of keepers
-57-75% profit from the sales of the hatchlings
And the owner of the male should get....
-Second and fourth choice of keepers
-25-43% profit from the sales of the hatchlings
Should either party want more than two keepers, they would have to pay the other party their share of the 'sale.'
So, in this case, say I have a lavender motley het snow female that I want to breed to a friend's lavender motley het amel male. Although one is missing a het, their roughly the same value. I intend to care for the eggs and female through the breeding process. By the end the day (yeah, right), I have 12 eggs that hatch to 2.1 opal motleys ph anery, 4.5 lavender motleys ph snow. Since I took care of the female, I get first choice of keeper and choose the female. The owner of the male (John Doe) decides to take the nicer of the two opal motley males getting second choice. I take the second male, and John takes a lavender motley female. Now we each have a pair. But wait, I fall in love with a little lavender motley female and want some color diversity in my collection. So, John and I set a price to sell the remaining lavender motleys for. He gets 33% of profit. Since I want that female, I give him 33% of her value and I get to keep her. But wait, he really likes a lav mot male, so he gives me 66% of his value and he gets to keep him.
See how this works?
The variables are for you two to decide. Other variables that could shift who 'deserves' what are things like...
-Value difference between specimens
-Whether one snake is being shipped out to another breeder
-Who cares for the eggs, or if there is split labor
-Double clutches
-Whether the female is being bred to another male that year (Sperm can be saved, and the paternity among clutches is mixed up.)
-Egg binding or if one specimen is comprimised somehow during the trade
Everything needs to be taken into consideration- vet bills, labor, hatch count, etc. Again, a paper contract can go a long way, even among friends.
Best of luck.