Should I give TCGplayer my SSN?

If you are selling and getting paid, yes, providing a tax ID such as an SSN or ITIN is a normal, legal requirement, not a red flag. US law requires marketplaces to collect tax information from sellers and report earnings on a Form 1099-K, so TCGplayer, eBay, and every legitimate US marketplace ask for it before paying out. Buyers never need to provide an SSN, only sellers being paid. Your information is handled through secure, regulated payment systems, not stored casually. If a site asks a buyer for an SSN, that is a warning sign, but for seller payouts it is standard. EvoMarket works the same way, collecting seller tax details through Stripe Connect, the same regulated processor used by countless online businesses.