If you walk into a salon doubtful you are going to get what you want and have a negative attitude about it you are not going to leave with what you want even if the stylist does just what you asked for. You came in with doubt, fear and negativity and that is what you will leave with. Isn't this true in all areas of our lives?
You should most definitely tell your stylist how you feel, what you like and don't like and even past services you received that you didn't like. They need to see the full picture to get to know you and what it is you are looking for. But attitude is everything, so go in with a smile and positive attitude and I can assure you success.
Are you being unrealistic about your expectations? We have to be honest with ourselves about what our hair will and will not do as well as what we have for time in our day to put into our hairstyle along with the budget we have to maintain our hair. All of these things need to be considered when trying to find the perfect hairstyle. I love when clients bring pictures to show me what they like and don't like. The problem is that most of the pictures in magazines come with gorgeous models with thick perfectly, styled hair. None of that is realistic for most of us. These models spend hours in hair and makeup and most likely have some sort of hair extensions. The photos you bring work when you understand that and realize you are not going to get exactly what the picture shows. If you don't realize that, or don't want to, then you just set yourself up for failure.