Really nobody like bad food right. But when you are traveling - you sometimes go, where all people go. The tourist hot spots. And most of the time there a lot of restaurants around this spots, like at the Deutsche Eck in Koblenz.
But not all the restaurants near a tourist attraction are good, even when they are crowded.
Some are too pricey for what they offer or just sell average food.
Now the local guide community come into play. With Google Maps and the ratings and pictures you can find the best spots for you. For example in Koblenz you have great restaurants directly located in the old town like Hanoi, La Mamma or Chaopraya.
Always when I am traveling and start to look for a place to eat, I check the ratings on Google Maps. So you will never be disappointed.
So for you next trip. Make sure you have Google Maps ready. And when you go out in your hometown. Rate the places you like. Maybe I come to town and I will be more then pleased to read your ratings and visit your favorite spots. 
Enjoy your day.