What's the stipulation on this?

I will even do a month to month stipulating it will roll over to a long term relationship.

No, @Chad Osborne, I believe they stipulated that it could only be transferred in sale to a family member. 

Not only will you need a letter of authorization from the seller, but I also recommend adding a stipulation to the purchase and sale agreement that he will provide that authorization in perpetuity. 

If you intend to assign the contract, then this needs to be included as either a stipulation or the assignable GAR form needs to be signed by both parties.

(Unless that is something you are considering- and if so, then I would make sure you have an attorney write up a vendor's lien deed and have all stipulations recorded). 

Any legal stipulation I could put on my rental contract to protect me ?

@Katherine RobertsDo you have the "promises" that he made in writing as stipulations to the deal? 

Does the seller stipulate that it's what he provided?

Most states DO have laws that stipulate brokering without a license is illegal, not the other way around, it is just that most wholesalers ignore the laws and do so anyways.