The buyer has very little incentive to make payments on the 2nd and there is very little recourse the seller can take against a non-performing 2nd.
The only real consequence to the buyer of not paying the 2nd mortgage is that his credit would probably get messed up.
As I understand it, the best legal remedy the seller could get would be a lien against the property. There would be no way to force a sale of the property or to garnish any of the buyer’s income.
The lien could remain in place forever. It would only have to be resolved during a sale or refi of the property.
So there the seller sits with a non-performing 2nd and a lien against a property that he no longer owns or controls.
That doesn’t quite sound like a win/win/win scenario to me even though the odds of it occurring might be low.
The only reason I would carry a 2nd is if the deal couldn’t happen otherwise. And then, after the 2nd had seasoned for six months I would sell the note at a discount. It makes more sense to discount the asking price of the property up front and find a buyer who doesn’t need an owner-carried 2nd.