Each of these are questions on the yiras shomayim of the individual. A magid shiur who will pasken items he is not knowledgable about shouldn't be trusted with bochurim. The guy who "learns all year" but is willing to decide on a baseless halacha may be better off with a year round job instead of learning and then serving treif. I question how much someone like that is learning anyhow. Someone ready to give a stamp on a camp will also do it elsewhere and his hechsher should probably be avoided anywhere.
Each of these are questions on the individual's chezkas kashrus and whether they can be believed for anything.
In fairness to some of the people involved - the pizza was a clueless 18-22 year old bachur, i have no idea how exactly the shayla was presented (if at all!) to the magid shiur, and I'm sure the shutaf would have been shocked at what was going on under his alegged auspices and was just relying on his trusted shutaf/B-i-L.
the owner - well just shows you how far monetary negius an affect you...
The point is the hefkeirus of the situation.
It is an understandable mistake, not quite mefurash, and we are meikal for bliyos keilim.
Not bliyos - same exact oil.