It's a very good idea to bar them. There was hoards of potential for some serious loss, even if the organizer has good intentions. Also, IMO people are trying to work off of OPM. (Other people's money) What this means, is they can organize a buy, build some profit for themselves and not have any investment of their own. This is not a always a bad thing, but if a person can't provide the product up front, what kind of contingency reserves does he have, in case he has collected and paid all this money and somthing goes wrong with the supply, or there are warranty liabilities? It's too thin an edge for comfort.
It's just not a good idea.