Help - What would you do??

[Pieterg]

I smell tuna or fish

[FrancoisC]

AND, lets not forget, this guy has now "modified" the frame by sanding the paint off.

ANY after market modification for whatever reason automatically voids any warranty in normal sales circumstances.

Must you now refund him and take back the frame in this modified state, sans paint?

Chancer - tell him he has no recourse due to the fact that he has now modified the frame. Case closed.

And if the paint had to be removed to identify a crack, how on earth were you to reasonably know that there was a crack under the paint.