I've done a lot of dual agency situations. When I worked for a builder, as soon as unescorted buyers came in I was immediately in a dual agency position. I ALWAYS explained agency to the buyers and maybe only twice did the buyers get another agent to represent them. I never have a bad experience with dual agency but have heard some of the horror stories. To answer your question though, there should be no extra cost. The total commission is the total commission, whether one person is involved or two. If you trust the person you've been working with, you are probably OK.