https://www.youtube.com/watch?v=iQuX_JzJ9bYI explain everything in the video, alternatively here's the story:
I started a trade for €100 of Steam Giftcards to Bitcoin, the seller says they were already used which they weren't, I show them a video of my recent top-ups on Steam which clearly shows I have not used the giftcards, I also show them the G2A receipts (where I got the gitcards from) with the time and date so they can compare everything. The moderator takes a whole month to reply and then rushes to close my ticket within 24h, he asked me to get a message from Steam Support. Keep in mind, the moderator replied to me on a Sunday, I don't think Steam Support works on Sundays. I keep them updated in the trade/disputes' chat saying that I haven't gotten a reply yet (Jan 6). The moderator closes my ticket on for not providing enough proof (Jan 7). This site is a scam and ultimately has really terrible support.