You're missing something.
The * groups are all open groups. Anyone in Socialcast can join any * group. The only way to admit vendors to a private area within the current Socialcast architecture is to take those groups private. It's pretty unmanageable at this point to do that with 161 members. I (or someone) would have to field member questions about what groups are available and add them to any they want to try on. Then when they drop out and want back in, we'd have to add them again. I can invite everyone to all of the groups, but they have to accept the invitation. If they don't, the invitation expires after a period of time. Yada yada!