1) They Know the Neighborhood
Good agents are extremely information about their neighborhoods and the marketplace problems that effect buying and selling. And if they don't know something, they know where to find the information within their local contacts.
They are able to compile the all important "comparable sales" of houses for the reason that immediate area and hand these facts to you so you can make a more informed decision. Plus, they are able to tell you about crime, schools, and other community facts.
However the big thing here is comparable sales. And that is knowing what similar houses have sold for in the last 3 to 6 months. Hossain Kabir
2) Use Your Agent as a "Buffer" When Negotiating
Top producing agents negotiate well because, unlike most buyers and sellers, they are able to remove themselves from the emotional areas of the transaction. Agents also take the awkwardness and uneasy feeling away if they make that offer that is way below just what a seller is asking.
Sometimes sellers get offended when you stand there and offer $30,000 significantly less than they are asking. But usually that is since they don't fully understand just why the offer is at a decreased number. But a agent could make the offer and explain why their client has come up with that figure.