You know brand new official PS2 controllers are still fairly widely available. I picked one up last year for about $30, seems to have gone up a bit since them, but certainly better than buying any used controller even if it seems fairly clean (peoples hands are grossssss).
Yes, I've got a couple of those, boxed, as well. The semi-see-thru color versions (graphite for example) are really great controllers, and always had a better feel to me, but they are a tad less durable compared to the stock solid black ones. (The DS1 versions of these...the clear see-thru...are absolutely great, too.)
I've had very good luck with used controllers (which I always clean top to bottom...and with a q-tip into the d-pad...so the previous user factor is reduced to wear and tear, not germs).
I'd say some of the ones I've come across are just pristine, and way better than the ones, say, that I leave out for couch co-op with friends. (ie. Similar to the quality of PS1 and 2 merch/games I've bought from Japan, which has been pretty awesome.)
It's not like they haven't been used, but more that whoever owned them didn't snack while gaming, basically, and respected their electronics.
Again, SF Bay Area is a bit of a cornucopia with this stuff because while there's a ton of janky, overpriced, beat-up stuff on CL, there's also plenty folks who are serious gamers who jump on CraigsList mostly to pass things on when they trade in, up, or simply move on.
Btw, I purchased the Sega Saturn Controller adapter for PS2 that the guy sells on Ebay and it worked out great value for the $$. (Legit, and helpful seller.) It's best for 2-D games, and arcade collections and shmups. I haven't noticed any lag at all. And, yeah, there's somebody else on Ebay selling new Saturn pads in groups of two. Had good luck with those, too.
Between the OG DS1 digital controllers, Saturn pads, DS2, light gun and a couple arcade sticks I'm in good shape on the PS2, but I'm missing the Namco NegCon and Arcade Stick, which I've always had my eye on but never bit on.