Under the laws of all states in this country a non-profit corporation can be sued just like a for profit corporation, limited liability company or an individual.From what you have written I do not see a factual or legal basis for you to be sued for real estate commissions concerning the rental situation. Custom and practice in the rental industry is that the landlord signs a listing with a real estate agent to represent him in leasing out a unit where the agreement states what the agent will receive from the landlord. If the property is listed for rent on the multiple listing service under the local association, then the listing agent by placing the listing on the service has agreed per a contract to split his receipts from the landlord in a certain amount with the agent representing the tenant if the lease is entered into.From what you have written, the landlord and/or his agent is responsible for the demanded real estate commissions, not you or your non-profit corporation.