Well, USPS people can only do so much, they don't handle the packages through the whole system. The boxes go through automated conveyors and various machines, who knows where it fell out. Its the seller's fault. USPS is great when handling the heavy flat rate boxes, but you have to pack them correctly. My 50 pound medium flat rate boxes make it just fine. You have to pack them tight, glue the box tabs together, use reinforced tape on all sides of the box and put extra tape on the corners. I would double box a lathe chuck and add extra card board around it to hold it tight.
I make bullet gas checks for a living, so my boxes can be very heavy. I can put 20,000 to 30,000 small pieces of copper or gilding brass in a medium flat rate. USPS only looses or destroys a couple per year, thats not bad. But, watch out for FedEx ground. They have destroyed a few heavy items of mine, like a nice old one of a kind ham radio tube amp that I could not repair. FedEx has been very rough on my packages, I avoid them when I can. UPS is far better in my area, I get my steel from them often and the heavy 70 pound boxes survive surprisingly well. But, I ship over two thousand heavy USPS boxes per year with very little issues. I wrap even the little small flat rate boxes with the reinforced tape on all sides if its over 2 pounds, lighter boxes still get all of the corners taped up.
I make bullet gas checks for a living, so my boxes can be very heavy. I can put 20,000 to 30,000 small pieces of copper or gilding brass in a medium flat rate. USPS only looses or destroys a couple per year, thats not bad. But, watch out for FedEx ground. They have destroyed a few heavy items of mine, like a nice old one of a kind ham radio tube amp that I could not repair. FedEx has been very rough on my packages, I avoid them when I can. UPS is far better in my area, I get my steel from them often and the heavy 70 pound boxes survive surprisingly well. But, I ship over two thousand heavy USPS boxes per year with very little issues. I wrap even the little small flat rate boxes with the reinforced tape on all sides if its over 2 pounds, lighter boxes still get all of the corners taped up.