Regarding the question of whether one must check an egg for blood spots, the Shulchan Aruch rules that one may eat hard-boiled eggs where checking is impossible. R' Moshe Isserles adds that checking is not required, but that a custom exists to check eggs if they are cracked during the daytime (when blood could be seen). A contemporary Ashkenazi authority writes that while "halacha does not require" checking supermarket-bought eggs, "there is a minhag" to do so. Nevertheless, eggs are not checked in commercial settings where doing so would be expensive.