The MLS system provides you with options, you can work with any REALTOR®.
That is right, if the property is advertised by one company, you can work with another and buy the same property. Sometimes it is a benefit.
If the house is listed MLS, then you have a flexibility.
How can you know if it is MLS? Most companies use the MLS system and if you have a question about it, contact Rick, he can get you the answers you need.