"The item was not in the envelope due to ... " (more) damage during transit; however, the seller was very patient and helpful. I hold the post office responsible for it, not the seller. "
"So sorry the envelope was damaged during ... " (more)delivery, thanks for sending pictures and bearing with me on this! Next time I guess I'll wrap the whole envelope in tape instead of trusting them to do their job correctly. "
"next time give the post office sufficient ... " (more) time to do its job, especially if tracking provided to you when it was sent shows it is in transit - instead of filing a dispute."