Are Convex Mirrors Useful or Not?

Every once in awhile, when I do grocery shopping, I see empty bags, packages and boxes of foods and clothes on the shelves at different isles of the store. Makes me wonder why these stuffs are empty? Could it be because some costumers decided to take or eat it with the purpose of not paying them afterward? If so, how could they get away stealing and robbing without getting caught? That made me think that maybe the store should have never installed convex mirrors at all; it seems to me that they are no help at all when it comes to monitoring what the people inside are doing. No wonder why this kind of problem happens for none of the thieves are caught yet. I guessed the security in that store is not being monitored strictly.