Friend of mine and his wife built their own home. Not just serving as his own contractor, but doing a lot of the work on their own at night. They were nearing completion, late one night working at midnight, guy stops by, rings the doorbell, and makes them an offer they couldn't refuse. They had custom made almost every square inch of the place, literally in seconds went from working on the house to negotiating a price. Next morning they agreed with him on a price and made a ~$300k profit. He said it hurt to let it go, but they just told each other they could get a nice house on the lake now.
He's just a money making machine, but he works his rear off. He had storage units as a side job and made a small fortune running that.