Purchasing Bikes
Whether you are purchasing new or used bikes, they both present issues.
Purchasing Used Bikes
This basically turns you into a pawn shop, and as a result you are subject to the same accusations -- such as accepting stolen goods.
Purchasing New Bikes
While most community bike organizations have an underlying goal of getting as many people on bikes as possible, most also support the re-use effort of refurbishing used bicycles. Purchasing something new fits with the first goal, but misses the second -- not to mention it may put you in direct competition with Local Bike Shops (LBS).