First, congrats on doing well in a Pokemon Card Tournament!
Now to address your question about trading cards.
I don't mind if you trade cards here. However, I do not play the card game or collect the cards personally, so I know little about it. Additionally, physical cards present more challenges than digital Pokemon games. In the digital games, you don't lose a whole lot when you trade a Pokemon to someone else and they end up ripping you off (you may have ended up wasting some time, but all in all relatively little). However, Pokemon cards can actually end up costing a fair amount of REAL money. Single cards can be worth 5, 10, 15, or even 30+ dollars and they are a lot harder to collect. This means if there is a mistake or mailing issue, this hurts people a lot more. Additionally, unlike with the virtual games, trades do not happen instantaneously, so it is harder to stop these unfair deals. Also, there is the issue of PO Boxes being a little more personal than sharing a Friend Code for your 3DS. These are all factors that make me a little hesitant about advertising this as a trading card thread, especially since I don't know much about the trading card game.
That said, feel free to talk about the trading card game here and request to make trades. The title of the thread technically just says "Competitive Pokemon Trading Thread", so I guess that leaves it open to Pokemon Cards as well. You may make a shop post that displays cards you are willing to trade instead of virtual Pokemon and I will link it in the OP. However, I will request that once someone shows interest in trading for one of your cards, take it to Private Messaging to discussion the deal further since card trades are a little more delicate. If you can make it work, I am fine with it though :]