Can a Jew give his Jewish friend a product which is kosher m'ikar hadin if the person giving it would not eat or drink it himself?
The product could be e.g., kosher meat which is not glatt, scotch which was finished in sherry casks, a snack with powder milk which is not halav Israel. All of these are considered kosher by major certifications (Rabbanut Israel, London Beit Din, OU respectively). But some people are stricter with themselves.
Does it make a difference if one knows if his friend eats of these products? Or if he tells him explicitly what the 'issue' is?