When you buy that title, you charge interest, in order for the person buying the mortgage from you not to lose, the real estate market must grow to meet the amount of usury. Now that cash that you traded for the right to let that person live there, what that is worth is based in nothing but people's faith in what it is worth. So in order for you not to lose, you rely on the faith of society.
I've bought titles where the other person lost money (compared to the market price) when selling. Maybe they gained something non-tangible like not having to maintain said item anymore, or they wanted cash to buy something completely different and took the loss to be able to do it sooner. Hell if I know, not my business.
Your assumption that they gain monetarily by selling it to me isn't based in reality. Their reason for selling isn't my concern, nor is them making a profit on the sale. I'll pay whatever I'll pay for my own reasons.
I don't care what they think it's worth in dollars other than as a starting point for negotiations. And I really don't care if they make anything on the deal. That's their problem to solve what they think they need before they say, "deal".
Assuming I'm "paying interest" to them to sell me something is a bad assumption. Price is negotiable. They don't like what I'm offering, they walk. I don't like what they want, I walk.
It also works the other direction. I let one of dad's collectible cars go for what he paid for it. My reasons for doing so were my own. They included that dad knew the buyer before he passed, they both shared a common interest in that type of car, I wanted to see the car used and not sit and rot in my garage, and that I knew the buyer knew what dad paid for it. I paid nothing for it, so there was no skin off of my nose other than diluting the value of his estate by a couple thousand bucks.
The buyer didn't "pay me interest". He got the car below "market" value. And both of us are fine with that deal.
Plenty of deals out there where the seller is willing to lose money for whatever reasons they have. They do require patience and an ability to search for them. There's no mandate of a specific economic model that requires growth.
Barter also bypasses all of that. If I offer to do something below market cost for you and you also for me, or trade goods straight up, and we are both happy with the results, there's no need for "growth", "interest" or any of the constructs of those selling or reaping benefits from transaction fees.
Your general assumption that every deal made in our economy is based on bending the other guy over the table, just shows a weird world view, probably enhanced by doing business with those who enjoy said bending. You need to find a better class of person to do business with.
