If you don't think you have, then you should probably be more clear and confident about that if asked about it by the authorities. Like, if police know that you have purchased fakes in the past (it's kind of unclear if they're aware of this?) than you should confidently say "I never sold or traded any cards that I purchased as fakes. Every card I traded or sold were real as far as I know and never had reason to believe they were fake" instead of " I might have and didn't realize" because the latter somewhat comes off as almost an admission of guilt that you don't want to fess up to. from my experience, saying the likes of "maybe I did but didn't realize" comes off as guilty as hell and when it comes to law, what matters is if it's been proven that you defrauded someone. Unless you can prove you didn't know they were fakes (which usually takes more than words) than you're SOL. Which brings up the point of not admitting to any of these sales or trades if there's no evidence of the sales/trades (e.g. email, text messages) until you speak with a lawyer. Without evidence, it's just someone making a baseless accusation against you.

I'm guessing that's what all this is about, though- that your being accused of having sold or traded a fake to someone, or to multiple people, and the store owner decided to try to bust you for it. If you won a tournament using fake cards, and won some sort of prize, you might be liable for fraud there but I can't say for certain... but if you honestly didn't have any fakes on you, but they find some fakes in what the guy went through, then you should presses charges for theft and try to get compensation, especially if you have pictures or receipts or anything that prove those cards were real. If not compensated (which isn't likely without evidence or a confession) it can at least help you out.