"Still, I have never seen a 1099-Int from a buyer issued to a seller for an installment sale, and they have not done this in prior years. They had been issuing a 1099-Misc for rent payments, and we finally got that corrected."

A situation could even require both forms. The 1099-Int really isn't an "installment sale" form; it's for Lending. The Sale is a separate type of activity.

And there might need to be a1098, too.

I have clients who used to buy "man-camp" trailers from the oil field, update them, and park them or sell them to mobile home park businesses, and often would carry the paper on them.