I think it probably works fine for national delivery couriers filling space in their van with additional extra bulky items; services to disintermediate them to move heavy goods for less cost than a dedicated courier already exist and some of them even wrap suitable insurance around it.

Internationally if it's P2P rather than P2companythatdoesthecustomspaperwork it's pretty much pure smuggling-as-a-service, and yes, people who kindly help carry the stranger's Colombian souvenir on their passenger flight for a small fraction of the ticket cost will find themselves being jailed at the other end.