Set the rate at 5.5% because it felt fair, then the best note bid was 68,500
I set the interest rate on a note I carried by feel and it cost me somewhere around 17,000 when I needed the money back.
The deal. Small 2 bed 1 bath rental, about 780 square feet, tired but fine, in a working class part of a mid sized market. I'd owned it four years and it was free and clear. Sold it for 96,000 to a guy who'd been renting two streets over. 8,000 down, so 88,000 carried at 5.5%, 30 year amortization, no balloon. Payment 499.68. I picked 5.5 because that was roughly what a bank was quoting on owner occupied paper when we started talking and I didn't want to feel like I was taking advantage of him. He's a good guy and he's never been late.
Eighteen months later I found a flip I wanted and I needed cash. So I went looking for someone to buy the note. Balance was 85,900. I had it in my head that a note with a perfect 18 month pay history sells near face. Three quotes came back. The best was 68,500. One buyer explained it to me plainly: at 5.5% over 342 remaining months, the payment stream just isn't worth what I thought, because they're pricing to the yield they want, and a below market coupon with no balloon means they're stuck in it forever. He also said the 8,000 down was thin and the pay history was young.
I didn't sell. I found the rehab money elsewhere at a worse cost and I still own a note paying me 5.5% for the next 28 years, which was a fine outcome for the buyer and a mediocre one for me.
What I'd do differently. Price the note as if I might have to sell it, because I did have to and I couldn't. That means a rate that reflects what I'm giving the buyer, which is financing he can't get elsewhere, and a balloon so the paper has a defined end date instead of running to 2053. Bigger down payment. And I'd have asked one note buyer what they'd pay for the note I was about to write, before I wrote it, which costs nothing and would have told me everything.