I see what you mean now.

I thought you were mainly concerned about shipping things from the US, which neither I nor anyone I’ve known has had intercepted or interfered with en route to dozens of countries, frequently containing valuables. It must happen, but it seems very rare.

The other way though, if you’re sending packages to the US from other countries, you could have that problem occasionally, which I have experienced twice and heard of from other travelers shipping things to the US.

As far as I know, that’s a one-way problem, US-tagged packages seem to slip through sticky fingers.