Pretty much my mail carrier is the same way. If I order a Sega CD or Sega Saturn game, even just a CD in a standard jewel case, it always gets cracked or broken. Frankly I don't know how the guy even has the job, he's over retirement age, and so out of shape that he can barely hobble around without running out of breath. So unless it's packed to withstand abuse, anything I order will be slightly damaged if coming from him. I've ordered $150+ games that he crushed (which weren't packed with any kind of thought).
IMO, as someone who often ships items. If it's very valuable, it absolutely needs a sturdy cardboard box to go in, with plenty of packing to keep it held tight in the center. Mailers can be scrunched and folded, sat on, or torn. No one should use a mailer for a fragile or valuable item, ever.