Seller Finance Exit Options - Negotiating

[Thomas Reilly]

I have a seller finance deal where the seller is agreeing to $300k (30year, $0 down, at 3.5%) so lifetime value of loan to seller is about $484k. If I refinance the house with a bank in let's say, 2 years from purchase, the seller only gets what the bank appraises it for correct? 

So if the bank appraises it for $310k, then that's what the seller would get?  

My seller is worried I'll refi fast and he'll miss out on interest payments (the main reason he wants to do this), so I'm trying to give him a way to see some upside in choosing my offer. House is in good condition, and is priced fairly. 

Any thoughts on a creative way to offer upside to go with me (assuming the math makes sense). One thought I had was offering "If I refinance with a bank and the value is appraised higher than $300k, we can add $X (let's say $10k) to what you would have gotten"