I have done a number of group buys (17j 7750 swiss movements, crowns, cyclops, etc.) and I am of the opinion as well that it requires someone to ultimately take full financial responsibility. In the case of the crowns I got them all and then found that a certain number were unusable and so I had to move the cost per unit up to ensure there were not unhappy customers and/or I didn't lose a lot of money. They can be a valuable resource to the community but you do have to tread carefully.