There was a startup years ago that tried this. They shut down because people were afraid to carry a stranger's package.

Airmule. (There may have been others).

From my recollection the issues were that it is against the terms and conditions of many carriers to bring packages for other people.

What was being shipped was also dubious - sure it wasn't drugs but it was often ASIC chips, strange hardware from China etc.

I don't think I would want to take any packages in this way, but I certainly would be worried about export control stuff.

This is not a viable startup to be honest.

Personally, I also would never trust a random stranger with carrying my stuff. Delivery companies have tracking systems and insurances.