Ordered a book from them. Got here in fine time, and "correct" book was received but... wrong *edition*. So... kinda entirely wrong book. So buyer beware, you need to check the very very fine print to ensure that what you're getting is the correct book AND edition, as they lump all of them into the same entry, and don't split seperate editions into their own entry.
Edit: within 10 minutes of me contacting customer response, they completely resolved my issue. So, the caveat above still stands, but also know that they are on top of things, and you really do just need to be Very Discerning. But, for the prices available, you could stand to save a lot of money if all it means is inspecting your purchase for an extra 30 seconds. I will be checking thriftbooks.com again for whenever I need a hardcopy book. Just, I'll be a bit more cautious.