In an attempt to diversify our income the charity where I work are currently exploring hosting adverts on one of our websites. (For context its not our main website, but one specifically designed for one of our key audiences with psychoeducational information.) We don't think currently we have the capacity or expertise to manage this ourselves (negotiating fees with companies etc) and would like to trial working with an agency but are struggling to find one. 

Does anyone else have ads on their websites and work with an agency? And/or can anyone recommend any agency to work with?