My luck with Buffalo is pretty much 50/50, both buying and selling.
Selling: Sometimes I make a nice little wad of cash, other times I bring in two bags of seasonally-appropriate clothes and they buy one thing. I had better luck selling things at the Buffalo in Albuquerque, for some reason. Both college locations... maybe I just had better taste in Albuquerque. ;)
Buying: There've been a number of times where I've spent over an hour here trying on tons of clothes and -none- of it fits me (at least, not ...decently). Other times, I have a particular thing in mind and find it immediately. For example: "I'd really like a pair of super-worn-in 14-eyelet Doc Marten boots in size 8.5. Oh, look... here they are!"
Yeah, some things are overpriced, but it's cheaper than what you'd pay for it originally and the selection is (generally) cleaner and a little more stylish than what you'd get at a thrift store.