Most guys package real good,- but think of the odds here, eventually there is always a chance something will get caught in a conveyor belt somewhere and break open.
I have worked as a shipper/receiver and done warehouse time as well, and these things happen. When you work that kind of job, you see people breaking belt jams with thier FEET half the time. I have also put in time at UPS some years ago, and people throw crap all the time, thats how it is. Heck, we had people throwing packages against the trailors to "accidentaly" see what is inside and if it was worth taking, if not then the box would either get shipped and taped up at the next location, or reported and taped up right then and there.
I'm sure USPS is much nicer, but occasionally I get squished packages. You will often find an envelope well taped etc inside your box, but again, odds. My guy that went down was around for years before this happened, around christmas time last year.
It is in everyones best interest for good packaging, so unless there is some half assed operation out there, everyone will do a decent job. Even if using a fake return addy, eventually you will ship from the same location again - and can be identified by someone and they can probably try to hold you/watch you and take your stuff out back and check the package to see what you are shipping, so of course they care about shipping quality for you and them.