Of course there will be 6 months where existing rules will apply, we will all be able to bring booze and cigarettes for personal use as we do now. No doubt we will want to take advantage of that concession before it gets stopped, but it’s not smuggling.
Commercial goods will go through the existing process, so I don’t see why smuggling would be more or less of a problem, except for Ireland.
Just how they are going to stop Northern Irish residents bringing illegal goods across the Irish Sea has not yet been agreed. As there will be no land border with the south a sensible solution would be, “you cannot take advantage of any concessions at home but you can’t bring it across the Irish Sea”.
That would suit the Irish, north and south, commercial goods get declared, mostly. Personal use carte blanche as it is now, the best of both worlds.