I would only buy shoes from an op shop if they are brand new! The Endeavour Shop here sells lots of brand new shoes and clothes as well,at really great prices. I often purchase gorgeous clothes there and they always get commented on! However,it IS a lot more difficult for me to find shoes there these days, as I wear Orthaheels all the time now as I find they really do help with my pain issues. In the past though,I often did get new shows from this store as well as clothes.
I never used to, but now yes, as sometimes they are just too gorgeous not to! Though as everyone else has said, they need to be fairly new looking. Just recently I got a pair that I could tell had only been worn maybe once, as there was no wear/scuffing on the bottom at all.