Where to find great quality used/marked-down office chairs?

I am working from home for the foreseeable future and would like to invest in a good quality office chair since I am now sitting in one at home for most of the day. The one I have now is old and cheap and not the best for my back or posture.

I'd love to find a used high quality office chair (like Herman Miller quality) without breaking bank. I've looked on places like Craigslist and Ebay, but I am not sure that what they are selling is actually Herman Miller brand or similar quality. Are there any reputable sites for used high quality USED office furniture?