It will be interesting to see if they also apply more customs scrutiny to checked luggage for air travel when returning to the United States. Right now they are not. But, if you go to places like Costa Rica, which has had high tariffs on many imports for years, they make you scan all of your luggage when you enter the country and will stop and scrutinize what you are bringing in. CR will also periodically have raids on retailers who obtained goods that circumvented customers via things like clandestine border crossings.
There will be some secondary challenges with enforcement of this as some decide to roll the dice, import illegally and hope to not get caught. If there is enough of a price difference between buying something with a high tariff in the US vs locally I can also see some people travelling to Mexico or Canada to buy some higher dollar smaller items if the cost savings offsets the trip.