A lot of the London candy store thing is about not paying the very expensive business rates to the council. They are all owned by foreign controlled companies which just go bust come enforcement time.

They are not much of a guide to bad areas, for example American Candyland (bad) is opposite Selfridges (popular). Streetview: https://www.google.co.uk/maps/@51.514156,-0.1516145,3a,75y,1...