I have included a web referenced linked to this answer that explains IDX in detail.
What you may be seeing is the sharing of listings in online "aggregators" like Trulia and Zillow. For instance, when you find a property on Trulia, the agent pictured in the box to the side may not be the listing agent, but an agent who has bought an advertisement slot. Some of these aggregators have legal agreements with real estate agencies and MLS services for the right to use the listings, but other websites do not, and are in fact using them illegally. Sometimes agents pool their listings with those of other agents on websites they share for more exposure. There can be any number of reasons you see the property on more than one website and associated with more than one agent.
If you're interested in the property, ask one of the agents to show it to you. Be sure to check that they are indeed a real estate agent: ask for their card, meet them at their office, look their name up in the list of licensees on the Nevada Real Estate Division Site. Any licensed agent can show you a home that's listed on the MLS (that's why it's on MLS.). If you decide you want it, the agent will probably put you in touch with the actual listing agent who will write the contract and take the deposits. For his work, the agent who showed you the property will get a rental referral. Many agents will not show rentals as they are too busy, and the rental referral rate is low compared to a sale, or will only show rentals to their established clients. Other agents thrive on them and use them to build their list of clients; who knows, that renter today may be a buyer tomorrow.
If the agent you met told you he is a property manager, or affiliated with a property manager, it is likely they are the listing agents for the property. Ask him if he is the listing agent. Agents are required by law to be truthful. If he evades the question, I would walk away. If you lease, the day-to-day business including repairs, rental payments, HOA complaints, etc, will be handled by the property manager's office, and you have a right to feel comfortable with that office.
Mike Pristow, Donna Hodge & Associates
2230 Corporate Cr. #250
Wardley Real Estate
One Source Realty and Management
Buyer / Renter Specialists
Cell - 702.501.0973
Website - http://matthewsellslasvegas.las.mlxchange.com