Set, rarity, and edition
Identify the set, the card’s rarity (secret, ultimate, ghost, and so on), and the edition (first edition vs unlimited). The same monster can range from a few dollars to a grail depending on which printing you hold.
Grade drives the premium
For graded Yu-Gi-Oh, the grade and grader matter — gem-mint copies of iconic cards and early-set chase cards carry steep premiums driven by thin high-grade populations.
Price from real sales
Value from recent realized sales of the identical card and grade. Slabline aggregates Yu-Gi-Oh comps and shows value by grade with sales volume, then tracks your whole collection with a live total and a 0–1000 protection score.