Another vote for Up & Running in the Triangle. They charge £10 for gait analysis if you don't buy your shoes from there (it's free if you do). Based on my gait analysis there were 3 brands of shoe that I could choose from and they were happy for me to try them on and spend as much time using the treadmill as I liked until I was able to make a decision on which I liked best. Ended up with the Mizuno Inspire 8s which have been great so far. They also said that if I found I didn't like the fit I could bring them back and try others. Couldn't be happier with the service to be honest.