On several occasions I have suggested inserting language in an LOI or contract that is similar to that of artbitration, escrow or title insurance where those are applicable. Let me suggest the following language to professionalize your Buyers Offers, LOI's and Contracts. Addressing the #sellerfinancing upfront with a professional solution improves the chances of being accepted and lets the Seller know you take #sellerfinancing seriously.
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Seller Financing Payment Processing - Clause

The parties agree that all payments related to the seller financing note shall be processed through Zimple Operating Corporation (www.ZimpleMoney.com).
The Seller shall provide payment instructions to the Buyer, and the Buyer shall make payments according to those instructions. ZimpleMoney.com will serve as the independent platform for managing and tracking these payments.
All costs and fees shall be paid by Buyer and collected through the ZimpleMoney.com platform.
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Planning drives you success,