I'm doing interviews for seasonal staff. Since actions speak louder than words, my favorite questions tend to all start the same.
Tell me about a time when...
...you went above and beyond the call of duty on your last job.
...you received customer service so great you had to tell someone about it.
...you had to work with another person to overcome a difficult obstacle.
...you were so proud you were almost embarrassed.
...you made a lasting impression on a customer.
Asking about a specific experience helps in a number of ways.
First, if they cannot think of anything, then they haven't done anything. Don't hire that person.
Second, details matter. The more detailed they are, the more the event stuck in their memory, the more they will create memorable moments.
Third, you get to see how they define those terms. If their answer to the second question was, "I got an extra discount on my clearance items because I complained about the stitching," you can get a pretty clear picture of how they will treat your customers.
Past performance here is an indicator of future performance. Ask questions that draw out what they have done. The answers are telling.
PS As important as it is to ask about their experiences, it is their character that you need to hire. I use those questions above to look for particular character traits. In the case of today's round of interviews, I was looking for compassion, drive, problem solving, and friendliness.