Never again.
A tiny bit of research and planning ahead will give you better results than this place.
In a futile attempt to save money on a show that's impossible to save money on (Penn and Teller), I waited until I arrived in Vegas to purchase my tickets because I had read that you could get a good deal here.
First things first: You aren't going to get a deal on P&T from this place. The "low" price they offer is only for balcony seats which you can find directly from the source for the same price. The good seats are either not available from them, or are going to be the same price, too.
Secondly, one of their fantastic reps told me on a Wed that they were sold out and that I would have to come back tomorrow. I asked if P&T were performing tomorrow (Thurs) and she said yes. On Thursday morning I went directly to the Harrah's box office since there was a long line at Tix and I had recently acquired a coupon from Harrah's. Turned out, P&T are dark on Thursday! I marched right back to the Tix chick and punched her in the face!
Ok, I didn't really punch her in the face. But I would have if I could.
The bottom line for Vegas shows is this: Know that the very best won't be discounted in any way, and that you such just suck it up and pay before you get to Vegas ('O', for example). Those that have been around forever and are less popular (Jubille, Diva's) are easy to get into cheaply. The Vegas coupon books have many 2 for 1 tickets so peruse those first.