He is trying to protect himself from being cut out.
Normally he gets a commission from the seller. If the seller at some point decides to do the whole transaction alone with you and cut him out, obviously he would lose, so he is putting that responsibility on you, in case you buy the laundromat directly from the seller.
You can agree to this condition under the condition that if the seller changes, then you no longer have any responsibility to pay him any commission; whenever you end up buying the laundromat (if you decide to buy it with no broker involved).
Hope that helps.