I have also never gotten an email like that. I would be concerned that it might be a phishing scheme. Type in their website address (don't use links provided in the email), log in, and check your account info. Frankly, I never knew they charged for just being a member. I've never actually bought or sold anything on Gunbroker.
Jim's Rules of Carry: 1. Any gun is better than no gun. 2. A gun that is reliable is better than a gun that is not. 3. A hole in the right place is better than a hole in the wrong place. 4. A bigger hole is a better hole.