To supplement my earlier post:

I think this could work perhaps as a community project, but not a business. When I was in Seattle, there was a volunteer organization working out of a shed to provide bike repair guidance and tools to people. They would also accept (mostly busted) donation bikes, repair them, and sell them for cheap to keep the system going.

I would imagine that this could work as something like that, but with a bit more emphasis on teaching. I'm not sure how you could get the "try before you buy" to work, in this context though.