Boy, I hate to throw a wrench into the works.
If the property is listed with a Realtor, that doesn't guarantee that the property will be in the MLS.
Our MLS rules say that single family residences, listed in the county of membership, and listed on an exclusive right to sell listing have to be inputted to the MLS.
This means that "Exclusive Office" listings, one party listings, listings that are commercial, multi-family, or vacant land are not obligated to be submitted, and listings that are outside of our county are also not required to be submitted.
However, it is our policy in our office to submit everything simply because of the exposure you get with the MLS.
I have found it's a bad marketing plan to keep listings a secret.