Sounds like you require a signature on all packages you send out, which would clarify if it is a delivery problem .
? do you receive any negative responses for sending packages with a signature required, by buyers that find it a hassle.?
Yes, I always get signature confirmation it is for my protection not theirs, just like the insurance. Oddly, no one has ever fussed. Perhaps I have been lucky. The only irate shippee that I have ever had was the guy in Canada that I shipped an antique bayonet to with the full insurance value. It cost a bit in custom duties because of the declared value and he got angry about it. That's a shame but you can bet if that bayonet had gone missing he would have expected me to pay for it.