The see through shipping materials are 100% the fault of the source. No wiggle room there.
The lost package(s) are up for grabs, because there's some deciding factors that could push the fault either way.
1). Did you send the correct address with your order? Seems like a no brainer, but it has happened (Fault: yours).
2). Does the source hand write addresses or use cut/paste/print labels? Hand written (Fault: sources).
3). When the first lost package came through, was the shipping information legible and correct? If so (Fault: USPS).
i've had the same thing happen with another source. i called USPS and they claimed my package had the wrong zip code. They rerouted it and when it showed up, the full address was correct, though it was hand written, it was still legible and correct.
i feel for you, man. That's a tough break and i think if everything you said is true (this is the internet, don't take that personal) then the source needs to reevaluate his shipping methods and should be here a little more often to address concerns for the members to see.