We do both! Our main business is building, rebuilding, and refurbishing batteries for Hybrid cars. However we are trying to move more into the DIY market, so we have been buying up a ton of Li-Ion batteries from recylers and whatnot.
We usually get them as complete units, pulled directly out of a car. From there we open them up, disassemble the whole thing, and pull out the battery modules. We usually dont tear the modules down all the way to the cells, because often times that actually reduces their value (in addition to being difficult and adding a ton of extra labor cost).
As far as your “as-is” question, some battery modules get fully tested (we have a pretty in-depth testing process that I can get more into once I can make my own thread), some just get a quick once-over with a volt-meter to make sure they are at a good storage voltage, and some are not tested or checked in any meaningful way at all. Each listing should tell you the testing status of that batch of batteries*, and the price will also reflect the testing (less testing = massive discount).
*I say “should” because some of the listings currently up were not made by me, and I have not got around to fixing them yet.