If we are bringing Gemaras I can also play the Gemara game. B”K 27b.
bottom line is my comment was to Goofus who said “”if you feel wronged you shoudl go to the courts” Al pi Halacha this is not correct In fact the very lashon of the siman in Shu”a where this is discussed is “Keitzad Oseh Din Leatzmoi” or “How a person can make judgment for himself”
In my first two scenarios there is no question the fellow can take his item back. The last case is arguable. Rema in the above siman bring Mordechai in Hamaniach as a yesh omrim that would arguably assur Lior’s action, (I only say arguable because I’m not clear on the difference between taking the item and another item. I will have to see Mordechai inside, it may be the case that in a store with an ssigned value to the item, it would be allowed)
However the first two scenarios are without doubt alowed. and Goofus’ assesment, and your blanket disagreement are wrong.