owner financing interest

[Anna Catron]

Owner financing is pretty straight forward, but what about when it's paid off in full.  If it's amortized over 30 years, the seller gets all the interest.  If it's paid off (via refi) in 2 years, do they end up getting the same amount of interest?  I'm thinking no, but in trying to "sell" the owner on owner financing, one of the selling points is how much more money they get via interest.  

What am I missing? Thanks!