As you might be aware you can get badly caught out in more benign places and circumstances, even doing the "old country" favour for people.
There's a bit of a practice around where we are for expats travelling up to /from e.g. the UK by road with empty space in their vehicles to advertise in expat media that they are willing to "courier" stuff for third parties......apparently works OK until you stopped by customs on the autoroute and questions get asked what's in that well secured box..which of course you've never opened....I understand then gets very awkward and somewhat nerve wracking as the crowbars appear.....
Carrying stuff in for a third party that you have bought from an outlet of your choice might be OK, anything else and I think you are right, your feet wouldn't touch the floor.