Feel free to edit this.

Like me, most of you have probably prepared a nuclear bunker's worth of rarer cosmetic cases in preparation for Halloween. From my own observations in-server, nearly all traders (and even most high-tier traders) still completely dismiss the importance of hoarding these cases and yet plan on brainlessly bee-lining for a select few (Gun Mettle Cosmetic, Quarantined, Gargoyle mainly) soon after Scream Fortress drops. A few people are catching on, but they seem to be mostly just buying in advance for their own unboxing, or are only doing cheap cases like Tough Break Cosmetic.

The meaning of this is that there's unlikely to be very much outside competition from anyone who isn't in this group (unless there's a hidden storage account somewhere in Ukraine with like 2,000 Gun Mettle Cosmetic Cases, but even then they'll likely only list on SCM), and the general population is effectively willing to pay any price for the top-tier cases. It's important that on update night, to keep the price high by only listing a limited number at a time and not your entire stash at once, and DO NOT UNDERCUT. The people I'm thinking of are probably smart enough to know that everyone will just match prices, and so all this does is shooting yourself in the foot.

And of course, early on, it's best to list on Marketplace because of the tradability of unboxes and easiness of buying in bulk. Price-dependent, Steam Community Market is also worth keeping an eye on. Direct trading has almost never worked out for me when selling cases. Just keep this optimal behavior in mind and we'll all have a very happy Halloween.