None of these places, diners, drive-ins, white table cloth restaurants, even Chinese restaurants, have any strict definitions. Any place can be anything it wants to be, which is to say, if they think they're a diner, then that's what they are. I'd say that the biggest problem any restaurant has to face is their customer base. That doesn't mean regular customers necessarily, although that's desirable and regular may not mean frequent. A fast food restaurant in the right place just off the interstate can do a good business, yet they may not have what you would call regular customers but they still have a customer base, in a manner of speaking. Thirty years or more ago, some old restaurants found themselves without customers when new roads were built that took the traffic somewhere else. That's exactly what happened to Colonel Sanders. But sometimes new housing developments along the old roads can cancel out the effect, if you can wait that long.