Held a 3.125% loan through a servicer transfer, an insurance non-renewal, and a seller who wanted out
Three years in on a sub-to and it's worked, so here's what it actually took rather than the version where you inherit a rate and go to sleep.
Acquisition: 1990s four bed in an inner-ring suburb, loan at 3.125%, balance was $196,800 at closing, payment $1,588 with escrows. I paid $24k for the seller's equity, $14k cash and a $10k note to her at 5% amortized over five years, $189 a month. House appraised at $268k for my own comfort. Rent $2,275.
Three things happened.
One. Month five the loan was sold to a new servicer. New portal, old autopay did not carry over, and the transfer notice went to the seller. She forwarded it eleven days later. I made that month's payment by phone with a $12 fee and it posted on the 14th. Grace period saved me. After that I set a calendar item for the 2nd of every month and I have never once skipped checking it.
Two. Month nineteen the carrier non-renewed the dwelling policy over roof age. I had 45 days. Replacement quote came in at $2,410 against $1,780, which pushed escrow and the payment to $1,641. I put a new roof on for $11,200 in month twenty-two and the next renewal came back to $1,940. The payment is $1,619 now.
Three. Month twenty-six the seller called and said her mortgage broker told her the loan on her credit was blocking a purchase and she needed it gone. This nearly ended it. My attorney and I sat down with her and her broker. What resolved it was that I had three years of servicer statements showing every payment on time and I offered to pay off her $10k note early at a small discount, $8,900, which improved her ratios enough that the broker made her deal work. She closed on her place. She stopped asking.
Where it stands: payment $1,619, rent $2,400 on renewal, note to her retired. The 3.125% against current rates is the entire reason this asset performs.
What nearly broke it was the seller's own borrowing needs, and I did not underwrite for that at all. What I'd keep is the on-time record. It was the only thing I had to hand her that mattered.