The guy I spot at the gym owns eleven rentals with no loan in his name

I've been learning how private money moves and mostly that's meant reading fund documents that put me to sleep. Then a guy I've spotted on bench for two years told me he owns eleven rentals and doesn't have a single mortgage in his own name.

I assumed he meant an LLC. He said no, they're in other people's names. The sellers'. He buys the house, the deed comes to him, and the seller's original loan just stays there and he keeps paying it. Most of them are in the twos and threes on rate because the sellers bought or refinanced during the cheap years.

I said that has to be illegal and he laughed and said no, it's in the contract, the lender can call the loan if they find out and they usually don't, and he's got a plan for the ones where they might. Then he said the part I didn't expect, which is that he tells every seller that risk out loud before they sign, because if they hear it first from a lender letter he's finished.

He finished his set and left and I sat on the bench with my phone typing "due on sale clause" with one thumb. Two hours later I was still reading. I don't know if I want to do this. I just didn't know it was a thing people did between sets at a gym.