I absolutely love this book store. I've been to the area a few times and have only ever visited Alcuin (which I also love). The selection of books is huge and fairly well organized. They seem to have a lot history, military and science books but their literature and art sections are also very well stocked.
Once you browse for a bit you can get the "lay of the land". They have sections of better/rare books. Some are behind lock and key, others are not. Suffice to say that there are some very expensive books in the store but also a nice selection of general used books. I would hesitate to say this store will yield a bargain but prices seem fair to me. I was after fine press books so I was prepared for rare book prices.
The gentleman who helped me was extremely nice and we chatted about a variety of topics during my several hour stay. Eventually the owner came in from his Mesa store and he was very nice as well.
I do understand how someone could have a bad experience in a store like this. It looks like a basic used book store but it's more of a collectors store. When I pulled up in my rental car I knocked over their sandwich board parking sign that was very close to the edge of the curb. I picked it up and went into the store. The initial reaction seemed to be one of slight annoyance rather than concern but I brushed it off and proceeded to announce my interests. Within minutes they were very helpful and friendly.
So that's my last piece of advice. I rarely find a bookstore without potentially grouchy staff. I'm not making excuses for this but I find the best way to diffuse this potential is to announce your interests right away. Even if it's general fiction or something very basic. If you're looking for a bargain tell them that - at least they know to steer you away from their rare books. If you want rare books you need to make sure they know that you know how to handle them - so that takes a little show of trust. I realize that this seems like a lot of work (it's not that hard, honestly) but spending time in a good used bookstore, where you can find some common ground with the staff, can be a lot of fun. I had a great time in this store. They know their stuff!