A couple thoughts regarding what might be in the lawyer written contract. Some years ago we bought a duplex where the seller provided financing. The payments were amortized over 30 years but the contract required a balloon payment a lot earlier than that (I think it was 10 years). Also, the payments were made to an escrow company who computed the interest and provided us with the form 1098 for our taxes. I assume they provided the seller with his 1099-INT. Good luck.