I often dine alone and have noticed that the service I get is much, much worse than when I am half of a couple or part of a group.
My latest for instance (one of many): The other day I walked into an almost-empty restaurant and stood near the door. The waiter immediately saw me and turned on his heel, went back behind the bar, messed about, talked to the bus person, and after a few minutes yelled across the restaurant "You can sit at any two-top." It went downhill from there - his idea of asking for my order was to walk up and say "Well?" And then there was the 20 minute gap between me getting the bill and his taking the money...
I guess to him and the other waiters who treat single diners rudely, we are *just* one person.
But I make the restaurant-going decisions for my group. Everyone knows I am chowish and love to find excellent places, so my influence extends to my partner and all our friends. And I know for darn sure that none of us will be going back to that place for any of our gatherings or celebrations.
I know that smart restauranteurs already have this figured out. Treat everyone well, even the humblest solo diner who comes in with a book and sits in the corner.