Large marketplaces (eBay and similar)
Best for: Graded singles, high-demand modern, widest buyer pool when you are selling — or hunting comps when buying.
Watch for: Fees, seller ratings, authenticity guarantees, and return policy vary by listing. Photos and condition notes matter.
Dedicated card platforms (COMC-style, break/dealer sites)
Best for: Browsing inventory without hunting one-off listings; sometimes storage or submission workflows.
Watch for: Platform fees, payout timing, and how disputes are handled. Confirm whether stock is owned by the platform or third parties.
Specialty online dealers / shop websites
Best for: Curated vintage, team sets, or shop-branded singles with human support.
Watch for: Reputation, grading standards on “near mint” claims, and whether prices track recent sold comps.
Social and group sales (Facebook groups, Discord, Whatnot-style live)
Best for: Deals and community finds when you already trust the seller or host.
Watch for: Higher fraud risk. Prefer sellers with clear return policies, tracked shipping, and payment protection.