Chris, good luck with the group buy if you move forward with it. There is a reason they are banned from most forums and it isn't because they work so well. The only way to do one is to get full payment up front and then hope and pray the shop comes through with the product. If you do one and pull it off without someone getting their feelings hurt, you will have the unicorn of group buys.
Interesting, I had no idea! Then again, I’ve never taken part in a group buy. You bring very valid points though! I’ll probably pass on that idea after all.