"As Is" is a retail and real estate term which indicating that the thing for sale is offered without any cleaning or fixing on the part of the seller. When the term "as is" is affixed to a classified listing of used or refurbished merchandise, beware.
As Is is frequently used in thrift stores such as Goodwill or The Salvation Army. So much so that in areas where Goodwill flourishes, there are outlet stores called an As Is store. At these stores there are no racks or shelves. Instead there are piles upon piles of clothes in bin after bin, all in a large warehouse. Such As Is thrifts are a godsend for thrift shoppers because everything is sold by the pound. Plus you literarlly have to dig through everything in order to find the cool threads. Shopping at an As Is store is an exercise unto itself, reminiscent of both a climb and a dig. Finding a pair of pants in your exact size takes a lot of luck; t-shirts are easier to stumble upon. Dresses and skirts abound, if that's your thing. There's undies too but who the hell buys their underwear used?
I know of only two true Goodwill outlet stores named As Is. One is in the Mission District in San Francisco while the other is in Burlingame, CA, just south of the San Francisco International Airport. I have been to the former location (at 86 Eleventh Street) and can attest that it is indeed heavenly. There are other Goodwill outlets stores—all of which sell stuff as is—many are listed here.
These outlet stores all seem to close early to mid-afternoon, so go before lunch. You'll need plenty of time to find the good stuff. Or go right before they close and grab whatever because you have to wear clothes.