Please excuse the bluntness of this language but in this case simple is better.  But this may make it easier to do group purchases.  Fundamental to purchasing as a group is the knowledge that the purchaser is not keeping any profit from the sale and is passing on the quantity discounts to the members who participate in the purchase.
 
 
1.  The group purchaser should describe the product, the part number if any, the qty pricing policy, the shipping policy, and where and when to pick up.
 
2.  Do not expect the group purchaser to deliver your product.
 
3.  The person who does the group purchase must get the money before the order is placed.  No money - no product. (think PayPal or check) Do not ask for COD.  (I'll pay for it when I pick it up.)
 
4.  There should be a minimum number of three members participating before the organization's name can be mentioned as the purchaser. 
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5.  Do not expect the group purchaser to handle your special tax exempt status differently than everyone else's.  If the product is taxable then everyone pays the tax.  Otherwise purchase it yourself and get the tax exemption.  
 
6.  Please do not expect the group purchaser to care for your product for any extended time.  (If it is live product then please pick it up promptly.)
 
7.  If you have questions about the product please do your own leg work to find out about it.  Simple questions to clarify the purchase are ok but do not ask the purchaser to act as your private teacher. 
 
The goal in suggesting these guidelines is to make the volunteer's job less burdensome so that we can do more group purchases. 
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