I agree that customer service is at the top of the list. However, I have something to add and not sure if it falls into these same criteria. However, the two things that turn me off the quickest is arrogance, and pushiness. I was on vacation last week and went into a train shop and the arrogance was so obvious that I almost walked out.
However, not having a store close to where I live, I decided to stay and look around. I bought a tinplate car only because it was a good price. While I was looking I was approached every 3-5 minutes asking if I needed help.
I explained that I was from out of the area, and just wanted to see what they had, and they did not take the hint. It was almost like my wife and I were being followed!!