Only three manufacturers of note for 3 rail O scale. There were lots of 2 rail manufacturers including Walthers, All Nation and others not to mentio. This was the period where HO started to flourish with the likes of Varney, Mantua, Gilbert and Penn line. I spent yesterday with my father, and he shared with me an acquisition of a Gilbert prewar catalog that had some amazing HO product.
To the topic, I would think a modern train store would need other business lines to be successful; at least if one was to only sell O scale. HO and N make up the bulk of the hobby and that is where any profit might be found.
