Foreign products arrive in a country at specific locations---most likely large seaports. Impounding and stamping these products as having X standard or Y standa

Foreign products arrive in a country at specific locations---most likely large seaports. Impounding and stamping these products as having X standard or Y standard isn't very different if the standards body is the singular federal government, or applying 5-10 different standards levied by states. Also, even if there is a federal standard, the states themselves are always free to set greater limitations---for example federal emissions controls on cars, versus California emission controls.