There seem to have been several people rumoured to be serving human meat down the years, but some such as Fritz Haarman, never had the accusation proved (although the brutal murders were).
However theres a few items which seem pretty well established of human meat being provided to unknowing customers in a butcher shop—for example.
The first I found was Adloph Luetgert, which seems to be a well established story. This chap only did it once though as a way to dispose of his wife's body
More recently the there was this story, of human meat being sold in a shop in Moldova. Supposedly though - they got the body parts from a local clinic.
The last story indicates a little bit of the problem with the idea of a demon butcher who slaughters people for sale, as in that tale they were illegally using parts from a clinic.
To provide a constant supply of meat for your shop by other methods would be clearly difficult.
I guess you would not get more than 40-50kg or so meat from each person killed (a Hog tends to make about 70% of its body mass into meat apparently, and I would be surprised if your yield from a corpse was greater).
Even a slowish shop would get through that in a week I guess (can't find average for this), so you would need to kill a person a week or two to keep your small shop adequately stocked.
Such a murder spree would be unlikely to be sustainable long term, if you are in a country with a police force.