Well, before I even get started I just want to remind ya'll that I TOTALLY disagree with this type of business.
But I feel if your going to do something, you should always do it the best you can. You should always be looking to find ways to improve your business, otherwise you will not succeed.
I see a large potential for problem with the personal checks that you receive from party members. I'm not certain how the finacial part of ya'll quote on quote business works, but if I understand it right, you get the money from the buyers then you have to buy the items from the company. So you either get cash or check. Cash is fine, you have the money, end of story. I'd suggest that you state to your clients that if they use a personal check that you will have to wait to order their items until the check clears. In addition to that, you can offer then the use of Credit Cards, besides people tend to order more stuff if they can pay for it later.
Paypal.com is an online paying system, you can link your bank account and credit cards to it. Alot of ebay users use it to pay for stuff. You can setup a buyers account and offer your clients the ability to send you funds via Paypal.com. Also Paypal offers a virtual terminal, this allows none internet using people to call up paypal and give them their credit card over the phone, and paypal send you the funds from their card. All money is covered by Paypal and so you would never be responsible for bounced checks.
Like I stated, I'm not sure how the billing works in your pyramid skeem, but Paypal might be a good option to look into so you don't have to worry about bounced checks.