The USA doesn't inspect every package -- almost all current tariffs are on the honor system. They could start by checking every 1 in 10,000 packages and then build up the system until they're spot-checking x in 100.
Customs doesn't even know what half the shit is. If I order a quarter-pound of palladium for $4,000 from China, but pay tariffs on 4 ounces of lead (say, $5), do you really think customs can tell the difference? They open the package, see a chunk of metal, and go "okie dokey". Yes, sometimes they'll whip out an XRP gun and double-check the alloy, but not for a completely random & arbitrary 4-ounce package.
This will happen for every. single. product.