I have no retail experience, so cannot respond with any knowledge, neither am I looking to start an argument. But it was never said that Adam's ma had a 'cartload of groceries'. She could just have had a few in a basket which would make any loss to the store minimal. I can also see the manager doing this as potentially causing less disruption than calling security and trying to bundle an enraged and unbalanced woman out of the store. Alternatively, maybe he isn't a good manager which is why he didn't do as you suggest.