The ones listed on the MLS do for sure. If you found an apartment that you wanted to lease to a client, you would have to agree to something personally with the PM and/or landlord or possibly even the client (charging them a flat fee for finding you the place). I am a property manager and have engaged in all of the above scenarios, however if you are looking to make residual money the only way I know is to get a cut through the MLS listings.