Asking if a stylist is good isn't likely to be that useful a question.
However, I don't think there's anything wrong in asking who is the best at cutting short/long hair, colouring, hair ups etc. depending on what service you require. If they say everyone is perfect at everything, I'd be more wary.
My current stylist is classed as a junior stylist because she hasn't got years of experience in that particular salon but she's brilliant at cutting short hair, which is what I want. I tried a couple of the more expensive/senior stylists in the salon but prefer my 'junior' lady as she has a real flair for cutting. When I first booked her, I had a free initial consultation and asked her lots of questions and from her answers, I knew she was going to be perfect for me.
I prefer to go to a salon rather than ask friends as the whole paying thing gets awkward as they don't like to charge me properly and then I feel I can't be fussy with them either.