Underwriting is what I do, so I want the mechanics rather than the encouragement. If I bring a contract to a network member and their buyer closes, who decides the split. Is 50/50 the default because it's fair or because nobody wants to argue. And what happens to the split if the buyer negotiates the assignment fee down after inspection.
50/50 is the default mostly because it ends the conversation fast, and that has real value when a contract has 14 days left on it.
The mechanics. On a referred deal there are two jobs. Acquisition is finding the seller and getting the contract signed at a price that works. Disposition is finding the buyer who'll actually close and holding them through to funding. In a typical arrangement the person who did acquisition and the person who did dispo sign a short joint venture agreement naming the split, then title pays out per that agreement at closing rather than one person collecting everything and paying the other later. That second detail matters more than the percentage.
Where the split moves off 50/50: if you brought a contract already priced correctly with clean title and a motivated seller, and the other member simply forwarded it to a buyer who was waiting, some groups go 60/40 or 70/30 toward acquisition. If your contract needed the seller renegotiated down 15k before anyone would touch it, the person who did that work argues the other way.
On your second question, a well-written JV agreement says the split applies to the fee actually received, not the fee originally hoped for. So if the assignment fee drops from 12,000 to 8,000 after the buyer finds a foundation issue, both sides take the haircut proportionally. Agreements that name a fixed dollar amount to one party instead of a percentage go wrong exactly here, because the shrinking fee eats one person's share entirely.
Have the JV template reviewed once by an attorney where you work. What an assignment can say, and whether the fee has to be disclosed to the seller, varies by state.