For this topic, I'm mainly referring to physical games but, I guess you can talk about whatever.
Recently, I can't recall getting any "good" deals, but...a few years back I did manage to buy one of my favourites, PopoloCrois on the PSP for $5 off of Gumtree. Which is basically like Craigslist. (My original copy that I had as a kid was handled poorly and I lost the case + manual.)
What's funny is that, even though it wasn't sealed, it did have a sticker around the case to stop you from trying to open it. (JB Hi-Fi here did that with most games every now and then.) Upon opening it, the UMD looked like it had never been touched as well as the manual. So, I was fairly happy about that.