Any tools to show benefits of seller financing?

[John S Lewis]

So I want to bid for a 2 family, but I don't have a lot for a down payment.  The numbers on the rental tool here at BP are great if I can offer 5% down, with a purchase price of 23% less than the offer.  Are there any tools here on BP or elsewhere that will lay out the financing from the sellers side?  In other words, beside using a run of the mill amortization calculator, what other tools can I use to get the seller to go for my offer?