I too made a genuine mistake only a few weeks ago by sending a fautly bike part to a fellow lister in the States. I was'nt aware at the time of sending to the fact that anything was wrong with it . I accepted his observations which I had obviously overlooked and apologised for my error. I was not able to send him a duplicate so I refunded his costs.
I had no insulting or heated mail, but just the opposite. He wrote back and told me he fully understood and accepted it could happen to anyone. At no time during did I feel he was complaining but his concern had this gone to someone who did'nt detect the fault it could have been more complicated.
I will be more careful in the future and double check , nothing like this has happened to me before and I'm only grateful this situation was resolved in amicable way.
Doug Smith
North Dorset
UK