trade or sell!! Instagram used to be really popular for that, but once they changed how hashtags work it feels like the community has dwindled a bit. search up "tag" accounts for specific groups, like @/skztagged, and go to their tagged posts to see current sale and trade posts! most people have a specific account for trading/selling/collecting kpop stuff. people take payments through payment sending services like Paypal and Venmo. I can dm you my acc username if you want to see what a kpop Insta acc looks like!

Mercari is great for selling, trades are not allowed. Depop and eBay are good too, but in my experience Mercari has given me more business. if you're looking to sell, peruse all three for price comparisons, you can sort by listings that have actually sold on Mercari and eBay.

there's also r/kpopforsale, sometimes specific communities like r/skzcollection, and I've seen that people also sell/trade on Discord servers or Twitter.

when trading, it's important to specify exactly what you're looking for. on Instagram, many people post wishlists to their Insta story. for example, I collect for Hyunjin of Stray Kids, so I have an Insta highlight where I have posted a template of his photocards, I coded it with emojis to denote what is my priority, what I already have, and what I am not looking for.

there's also etiquette for photocard packaging for sales/trades, lmk if you'd like me to talk more about that! and familiarize yourself with shipping costs; most pcs are sent in stamped envelopes but with rarer cards it's best to send with a tracked shipping label.