Option agreement to buy the property back???

[Marcus Vega]

My brother bought a house owner financed a few years ago and the property has gone up in value since then. He was thinking of refinancing or selling but when going through the paperwork he found a page titled "option agreement for purchase of real property". It states that if he sells or refinances, the guy he bought it from has an option to buy it back at 25% of any increase in property value. I've never heard of anything like this. Has anyone else? Any thoughts or suggestions on how he can get the most out of his appreciation?