Half Priced Books is technically a second hand store, so as far as selection and quality goes I suppose it would vary store to store. It all depends on what people have brought in and sold to the store. In regard to comics, on occasion I have found some hidden treasure there. It is a decent place to check out if you are trying to hunt down some back issues, though they may not necessarily have what you are looking for. Most of their comic issues go for $3 and under which is some cases can be a pretty good deal for older issues. Their trades and graphic novels typically go for approximately half the retail price. The only problem is, they don't tend to pay much attention to the condition of the comics they sell, so in some cases you may end up paying more than the book is worth if you don't check to see what it is going for online.
They also sell movies, cds, vinyls and stuff along those lines.
The one that is near my house has pretty good service overall. Basically what you would expect from a typical book store.
That sounds like the BMV bookstore chain in Toronto. 40% off US cover but they sell a lot of remaindered stuff usually. They also get shipments direct from Diamond now and they retail cheaper than Amazon.
It's the one place I will genuinely miss when I leave this city.