The B'datz, Rav Karelitz, Rav Landau, Reb Chatzkel Roth, Lakewood Satmar Dayan, Shlita among many others including Reb Moshe Feinstein, Satmar Rav, etc always encouraged others to be present by the mechiras chometz. The observers may bring something to the Ravs attention, and it should be a publicized event- Unless the Rav is afraid that his mechira is questionable at best, then he hides and doesn't allow anyone to be present as one Rav in Lakewood has been doing for years, does not allow anyone to be present. Is the mechira valid?
