I'm not sure of your question, but I'll give it a shot. A listing agent has a contractual relationship with the seller and is expected to look out and act in the best interests of the seller. A buyer's agent, whether they have a buyer's agency agreement or not (may vary in some states) is expected to look out of the best interests of the buyer. A dual agent is expected to represent the best interests of both sides equally.
Personally, I don't practice or have much faith in the concept of dual agency. I will sell my own listings but I both verbally and in writing clarify early on that I only represent the seller in the transaction and to keep any confidential information confidential.
These are the basic outlines of what is expected. It should be noted however that there are breeches of these understandings. The buyer and seller should tread carefully and use good judgment in their choice of an agent and what you trust them with.