So what's being suggested is a way to rate groupbuy participants? I'm all for it. Get downrated often enough by groupbuy organizers and maybe you won't be invited to groupbuys at all. That would keep people honest. But -- someone could just create a new forum account and their rating is back. There would have to be some kind of verification process, which would be time-consuming; which would probably mean making GH a pay-for-access site.
Or maybe make a sister site to GH; GH remains a free, open forum, but a secondary affiliated site requires some nominal amount for membership, like any other buying club. Maybe make GB organizers pay a bit more, but they get access to some awesome services like rendering (Kaporkle as an example), and more intuitive ordering tools (Matt3o's system). People who would want to buy into the groupbuys would have to pay some nominal fee, enough to discourage people from just making up new accounts, and they would have to be verified in some way by the owners of this secondary site. Ordinary users would get tools as well, showing what parts of each groupbuy they need to get in order to outfit their keyboard. It would be great to have a drop down menu specifying your keyboard, and getting a report back indicating you need to get Kit #1, #3 and #5.
Make it a pay-for-play site, and make sure everyone gets what they want. (within reason)