So, my mom has most of the floor covered waist deep in stuff she doesn't need or use. She won't throw stuff out, but would be slightly less dis-inclined if she could sell it. A large proportion of the clutter is clothes, though there is plenty of other stuff. She needs to get rid of it (it's not her house), and I was wondering if there is any place that will buy large quantities of used clothes and stuff. I was wondering if anyone knows of such a place. She lives in Dunkirk, NY.

The obvious answer is Goodwill. After that, start looking around for consignment shops. You may get lucky there.

eBay. Seriously, if you just had an auction for "Garbage bag filled with clothes" with a picture of what's inside, some schmuck would probably buy it.