I have been doing my own and other people's hair for years now, and I get almost all of my supplies at Sally's. They almost always have exactly what I need, except for the rare occasion, but that can happen anywhere. All of the products I have bought from there have been great, and all of them have been good quality. The only thing that annoys me is that the staff seem to think they know everything, and have given me wrong advice and argue with me just to make a sale, even when I've made it clear what I want and that I know what I'm doing. But there are also some quite lovely girls there too, so it can be a chance as to who you get.

While the store is not very large, the inventory has pretty much anything you could be looking for!
In my personal experience, the staff I have encountered (Ottawa, Canada area) are not very knowledgeable when it comes to hair color and so when I've had questions, I rarely received any helpful tips so I've had to rely on myself which, is OK as I do know quite a bit about hair coloring. However, for the person who is not familiar with hair color, this lack of knowledge by the staff could cause a problem.
Over all, the staff are always friendly and will try to help you as best as they can!