How to know if a baseball card is worth money is three questions asked in a fixed order, because the first can rule the card out before the others matter. Is it scarce, is it sharp, and is anybody buying. A card that fails the first question rarely recovers on the other two.
Scarcity first, because it is the binding constraint
If millions exist, no amount of demand will lift the price far, because every buyer has many sellers to choose from. Look for a stated print run, a documented short print, or a date from before production rose. If the card has none of those, it is almost certainly common and the remaining questions will not change that.
Condition second, because it does the rest
Once a card is scarce, condition decides most of the price, and the difference between a sharp example and an average one is much larger than the difference between an average one and a poor one. Assess yours honestly and then read sales for that condition rather than for the best examples.
Demand third, because it is the one that moves
Demand is the question completed sales answer. Five recent sales tell you there is a market and roughly where it sits. No sales tell you there is not, at least not right now, and that is the honest reading rather than a sign to look harder.
Then settle it with the checker
When the card clears all three, five sales through the card value checker give you the figure and the spread. When it fails the first, you have saved yourself the search, which over a whole box is most of the time you would otherwise have spent.
Questions people ask about how to know if a baseball card is worth money
Can a common card ever be worth money?
In exceptional condition, sometimes, because sharp examples of common cards are scarcer than the print run suggests. That is the case where grading arithmetic occasionally works out on an ordinary card.
How do I know if a card is a short print?
From a published checklist for the set. Nothing on the card itself usually says so, which is why checklists exist.
Does a card have to be old to be worth money?
No. Modern numbered and autographed cards are the other half of the market, and some of them are worth far more than most vintage.
What if I only have one card?
Then this takes a minute rather than an evening. The order is the same.