Ok folks, I guess I have not made myself very clear. So I'll attempt to do that as politely as possible.
Oh, I think you've been quite clear. The problem is that, despite being clear, you're still completely in the wrong with this transaction and refuse to own up to it. This can all be cleared up VERY EASILY.
1. OP takes potentially defective lens to an independent camera shop for diagnosis.
2. OP posts results of said diagnosis, with supporting documentation.
3. If the lens is broken, offer him a refund. If the lens is fine, you're proven to be correct.
4. Move on with life.
You, of course, won't agree to this because you obviously knew about issues with the lens. There is absolutely no other reason for you to decline such an arrangement. Don't start sputtering about how the OP will intentionally damage the lens just to get a refund, either. Any decent camera shop would be able to spot that and it would also be pretty difficult to damage only the auto-focus feature.
