What is the ruling on purchasing meat from supermarkets without knowing the religion of the slaughterer and the method of slaughter, and what is the ruling on dairy and cheese products that are suspected of containing pork derivatives, and is it obligatory to meticulously research the ingredients of everything we eat?

Allah has permitted the slaughtered animals of the People of the Book if they slaughter them according to the Shar'i method, by cutting the two jugular veins and the esophagus. However, what is slaughtered by stunning or strangulation is carrion, and it is not permissible to eat it. If it is highly probable that the slaughtering was done according to the Sharia, then it is permissible to eat; but if it is highly probable that it was not, then it is not permissible to eat. If the matter is unknown, the basic principle is permissibility. A Muslim should seek out what is lawful and abandon what is doubtful. There is no need for an overly detailed investigation into ingredients.