I think there are too many eating places masquerading as restaurants .... they look good, which may be why customers are drawn in - initially - - but there may be no menus available to browse before deciding whether you want any of their food, service is not good, and generally the food is not good, frequently having been microwaved after being prepared well in advance, and - the prices are high. Another possible clue is the amount of customers they dont have sitting down! (and - clean loos are very important!)
Yesterday a friend and I went to the Notting Hill Gate/Portobello Road area - we passed a very busy Church cafe (slightly hidden away), which had lots of fresh salads and appetising looking food, yet just around the corner, a rather nicer looking eating place - with only one other couple inside - (we should have taken this as a BIG clue!) We had to ask for a menu as there were none on display anywhere and having had a mental blip we, stupidly, decided to eat there!
When the dishes arrived, they were either tasteless or too salty and pretty small portions. The waitress wasn't that interested, as we had only ordered 'snacks' of humous and tappenade, and roasted (?) vegetables, and a jug of water. It was certainly not good value for the amount on the plate - apart from which they were not tasty at all.
Even if customers dont complain at the time, people tend to vote with their feet, and if restaurants/cafes dont try too hard - they'll get the same response from the public. You may go once, but wont return. I think we definitely need to complain more!