Quite simply they have access to information you do not have. They get this through MLS and, more importantly, relationships with the other realtor. Please note this all goes for a good realtor... Many are worthless. A good realtor will take advantage of a bad one or someone not represented by a realtor in these transactions as they are not as simple as most think. example: buying realtor calls selling realtor and says "house is partially empty, mostly man's clothes in closet but pics of a couple on the walls, what is going on?". Selling realtor (who is not a good realtor) says "wife left the husband after he lost his job, he found work but in another town and moved to an apartment, thankfully he doesn't owe anything on the property". Buyers realtor now has the upper hand and negotiations will cost the seller money.