"Quick to criticise, slow to praise"

If I get really good service, I think the most important thing is not just to thank the individual but to go to the top, preferably the CEO, and let them know.
I worked in Selfridges for a short while, early in my career, and have seen just what crass complaints the public make, particularly when they know you can't respond: It's influenced me into taking this stance ever since.
Not that I did it for that reason, but it got me a free flight to Venice!