You take a sample of a charge and test it. If it contains forbidden substances you fine the importer. Most grocery chains in Germany with the exception of Ede

You take a sample of a charge and test it. If it contains forbidden substances you fine the importer. Most grocery chains in Germany with the exception of Edeka (I guess it's similar in other countries) apply stricter standards than the legal limit anyway with their suppliers, and ensure compliance by testing on their own