I do the same at restaurants; ask to see the manager then tell them that my server has been extraordinary (when they have been). I try not to do this when it's

I do the same at restaurants; ask to see the manager then tell them that my server has been extraordinary (when they have been). I try not to do this when it's obviously busy, etc. I also don't try to fool them with a stern "see your manager" demand then trick them.