Shouldn’t the question be: May a shopkeeper use force to stop a thief who runs off with merchandise that wasn’t paid for? I believe the answer is in almost all legal systems is that the shopkeeper would be charged with murder for killing the thief, though in countries such as the USA the shopkeeper might be acquitted due to jury nullification (but don’t count on it).
There is a reason that one of the first mitsvos, applicable to goyim as it was one of the mitsvos of Bnei Noach, is to have a legal system. Settling disputes over trade good by blood feud is not a good policy.