How to tell if baseball cards are worth anything is a question about a collection, and collections are answered by sorting rather than by searching. The routine below uses only what is printed on the cards, takes about twenty minutes on a full box, and leaves you with the short pile that is actually worth pricing.
Pass one: pull the numbered and the signed
Anything with a serial number showing a stated run, and anything with a signature applied during manufacture. These are the cards where supply is either disclosed or naturally limited, and they are worth checking regardless of who is on them. It is usually a small pile.
Pass two: pull everything that is not a base card
Inserts stand out: different finish, different numbering, their own set name printed on the card. They were seeded at lower rates than base cards, sometimes far lower, and in the overproduced decades they are where nearly all of the value in a box sits.
Pass three: pull anything before about 1980
Older cards came from smaller runs and survived in worse condition, which makes sharp examples genuinely scarce. Sort this pile again by how clean the cards are, because at that age condition decides most of the price.
Then price the piles, not the box
For each card in the three piles, five completed sales in your condition through the card value checker. Everything that did not make a pile goes back in the box as bulk, which is what it is, and you have spent your evening on the cards that could repay it.
Questions people ask about how to tell if baseball cards are worth anything
What if nothing makes the piles?
That is a complete and common answer. Most collections assembled for enjoyment contain no cards of significant value, and knowing that quickly is worth something.
Do I need to know anything about baseball?
Not for the sort. It reads the cards rather than the careers, which is why it works for an inherited collection.
Should I keep the bulk?
It is worth very little and costs nothing to store. Some people sell it by the box; most keep it.
Is it worth photographing everything first?
Only the cards in the piles, and then mainly for listings. Photographing a full box is a large job with little return.