How to incentivize brokers in 100% or close to 100% seller financing deals?

This response is based on a bunch of assumptions that might not be applicable here, but in the spirit of trying to be helpful: broker contracts are typically written in terms of total consideration i.e. based on all of the instruments that go into the deal. If you're signing a seller's note for a certain value, that's part of the consideration and is included in the calculation of the success fee gets paid on that. If the broker doesn't have a contract in place then you can either go around them (sometimes this is justified, sometimes not - in any case, that's the broker's mistake) or negotiate anything that is mutually agreeable. Yes, the seller still also needs to pay people who advised on the deal. Theoretically, the type of financing doesn't impact that. Practically, there's little harm in attempting to negotiate advisor fees. It would annoy me, but I always have the option of sticking to terms of my current contract even if it kills the deal.