Ideally, you'll select a buyer agent who will represent you fully during your purchase experience.
You want to find an agent who is quick on reply, gives great information and is an asset to you. This person will represent you first on your behalf, not the seller.
Occasionally, you'll find a home with your buyer agent that they may be the listing agent on also -- that is a dual agency situation.
Many buyers feel that they can "get a better deal" by calling the listing agent -- and this is false. Commissions are pre-negotiated, and if you call the listing agent, their first responsibility is to the seller, not to you.
If you want to learn more or have questions, please feel free to check out my website below or give me a call. I have many references I can share :)