The Multiple Listing Service is essentially a huge database including every home thats listed for sale throughout the entire region. Many agents would like to have you believe that they are the only person with access to this information. The truth of the matter is that any licensed real estate professional has access to MLS and can give you information about any house listed for sale.
Why this is important is because real estate advertising, including MLS listings, is generally designed to generate leads for agents. If youre unaware that any licensed real estate professional can provide information regarding the advertised home you're interested in, chances are youre going to call the agent who advertised the house, right?
Heres the problem: this is choosing your real estate representation by default. You know nothing about this agent other than the fact he/she advertised a house that piqued your interest. Further until such time as an agency agreement is signed between you and the agent you've just called, that agent owes fiduciary responsibility to the home seller and is working in their best interest, not yours.
The better alternative for a consumer is to have an agent with whom you have built a strong working relationship, just as you have a family doctor, accountant or lawyer. This is someone you know, trust and feel comfortable with. Then, the next time you see John Doe advertising a house, rather than calling him, you call your personal agent. That way, not only can you trust any information youre given, you avoid calling a complete stranger and most likely avoid ending up on another mailing list.