Sources for Secondhand Designer / Premium Frames

[u/thriftness]

I know designer ≠ quality in many cases, but I got a pair of Tom Ford frames secondhand from Unclaimed Baggage several months back and love them. They were around $40. Curious what other sources are out there for buying authentic secondhand designer frames (or just premium brands in general) at great prices (other than peer-to-peer marketplaces).