Two structural things to settle before the fee percentage.
First, define the base. "A share of the assignment" is ambiguous the second a deal double closes, because now there's transactional funding cost, a second set of settlement charges, and possibly a price reduction negotiated at the table. Write down whether your cut comes off gross assignment or net after those costs, with an example calculation in the agreement. On a $30,000 gross with $7,000 of double close cost, a 30% share is $9,000 or $6,900 depending on the answer, and that argument will happen on the deal where everything else already went wrong.
Second, decide whether you're ever a party to the contract. If you're outside it entirely you have no standing when your wholesaler decides to close on it himself after you produced the buyer. Some operators handle that with a JV agreement that names them on the deal, which strengthens the principal argument on the licensing side too, and simultaneously puts them on the hook for the earnest money. That trade is real and it's worth pricing.
On the buyer side, keep a record of what you told each buyer about condition and numbers. Claims against dispo operators usually come from an end buyer who says the rehab scope or the rent figure in your email was represented as verified. If you're passing through your wholesaler's numbers, say so in the email in those words, and don't restate an ARV as if you pulled the comps yourself. That written trail matters more than any policy you buy, because coverage disputes start with what you actually said.