Ebay, occasionally yoox (mostly shirts, if I'm being honest). I'm wearing wool margiela trousers at the moment that have a fantastic cut and were only $62 from yoox. For ebay, there are a couple periods a year (March, ~July?) where people unload their shit to buy new-season gear and seem to get kinda desperate.
Unfortunately, this strategy has been useless for Rick. I've been contemplating a basic tee for $160 all week which is probably insane.