Door-to-Door Fish Salesman

Today, the kids and I were in the backgarden (which is actually our front garden though we never go in that way) when a man came through the gate saying he was selling fish and would I like to buy some.  Puzzled and slightly bewildered, I said, "No, thank you.  Do you come by often to sell fish?"  He said every two months or so.  I asked for a leaflet and got a photocopied list of the fish he sells.  After he left, I called John's mom to make sure he wasn't coming around to steal our VCR.  She doesn't buy from door-to-door salespeople but has heard of it.  We talked about how you don't really know the quality of the fish, how old it is, etc.  Are there health and safety regulations and quality controls they must abide by?  Are they a registered business?  It seems kind of like an ad-hoc business to me.  Do they have regular customers?  This all just struck me as unusual.