I like an icon or symbol that is clean and easily recognizable. Two arrows going in opposite directions could symbolize books changing hands. An arrow going in a circle could symbolize recirculation. A handshake could symbolize making a deal. Textbooks, badges, leafs, and banners could symbolize college.
I know the major focus of the website is textbooks but don't forget about the broker aspect. When I think about a broker, things like bold, aggressive, and go-getter come to mind. Someone that has connections, makes introductions, and puts deals together.
A lot of designs are incorporating a textbook, which is fine, but I wouldn't mind seeing some with a small picture of a broker (guy with glasses and a tie, maybe sitting at a desk, writing or on the computer or the phone, etc).
Also, having "my", "text", and "broker" in different colors or just "text" in a different color than the other two seems to help people realize its 3 different words even though they're ran together in the URL.