1-2% of packages are estimated to get lost or stolen. those numbers are even higher for private mail services like UPS or fedex
the bottom line is this: in the end the sender has the responsibility to get you your package. if it doesn't get there or is stolen or a fire burns down the mailmans truck, etc... then they should make good and reship or refund. that is the standard practice... also youtube porch pirate videos, there are people that make a living literally stealing packages off peoples front door/patio and then selling online. if you have a porch pirate problem where you live simply get a PO BOX and have packages sent there instead or pay more for signature confirmation
i have found that chasing down the package by talking to the mailman or going to the post office it left or is going to, sometimes will result in them finding it in some bin or under the mailmans seat etc. i'm a pest and if you hassle them enough they will put in the effort to find it.