On a business lease you should have no problem getting paid.Many forms used in commercial are drawn up contracts by attorneys and not the real estate association forms.
I would consult your broker and make sure they ALLOW you to do these types of transactions and I would also have an attorney review the documents to make sure your commission and the broker's company is protected.
In some states including mine Ga,we have what's called " the commercial lien broker's law".
It does not apply to agents only the broker can file.If the seller or buyer tries any funny stuff I can file a lien making the property unmoveable until my lien is paid.
Closing attorneys on commercial always look to see if there are any commission due as they fear the lein law and know what can happen.Even if someone agrees to pay you in a seperate agreement have that agrrement referenced in the contract.For instance Brokerage commissions:Buyer is responsible for all commissions and Agreement "A" is hereby attatched and referenced herein and part of this "purchase agreement".Parties agree Commission will be paid in full in cash at closing as a condition of closing.
No legal advice,talk to an attorney and your broker.