For example, I took my girlfriend to a nice hotel for our anniversary last year. When the hotel heard I was having an anniversary, they sent up a very nice hand written congratulatory card, a bottle of prosecco, and a selection of deserts on the house. That couldn't have taken them more than 15 minutes and cost them like 20 dollars, but it is something I will always remember; I will definitely return there in the future; and I recommend that hotel to any friends seeking a nice place to stay. That is great customer service.
At a more basic level, I was at a mid tier hotel a few weeks ago and somehow I didn't get the room upgrade I paid for. The management immediately refunded me the difference without complaint and gave me a few drink tickets to use at their bar as an apology. That is good customer service.
Contrast those to my experience at my former favorite steak house this year where for the last ten years I had been telling everyone to go. I went there for Valentine's day (had a reservation) and was told I had to wait 30 minutes for a table to open. While I was waiting, I saw multiple couples of the same size come in behind me and get seated. After the 30 minute wait, they tried to seat us at the loud and noisy bar. When I complained, they basically told me tough shit you get what you get. A reservation just guarantees you a table not a good one. I concluded that they were discriminating against us because we are younger than the average clientele there. Not only did I walk out and cost them my business, but I gave them a scathing Yelp review, and now shit talk them at every opportunity. I will never go back even though they were great every other time I was there, and instead always point friends to one of their main competitors when asked my opinion about local steak houses. I do this even though I know the competitor's food isn't as good. They could have given me the table I deserved; they could have comped some drinks or something; but no, they were right and I was wrong and so they lost a loyal customer instead.