Most people selling cards don't know what they have. You do. That's your margin.
Facebook Marketplace, garage sales, card shows, Whatnot streams, estate sales. Find someone who needs cash. Buy their cards for a fraction of what they're worth.
Clean cards. Use a loupe and light. Identify grading candidates. Submit to PSA or CGC. A PSA 10 on the right card can be worth 5–10x what you paid raw.
List the slab, not the raw card. Better presentation = better price. Ship with semi-rigids. Reinvest every profit until the habit is locked in.
Raw cards are priced by emotion and urgency. Graded cards are priced by population, condition, and market. The gap between what someone pays for a raw card and what a slab sells for is where you operate.
Grading fees $17–$300 depending on service tier. Do the math before you submit.
Once trust builds, people send you their cards to grade, photograph, list, ship, and sell. You charge 15–25% commission. No capital required. Inventory scales with reputation.
This doesn't require a warehouse. It requires a process and a reputation.
"Most people try to create a brand before they create cash flow. Don't."
Your plan is already right. The execution starts when you're ready.