How to know if baseball cards are worth anything is a sorting problem before it is a pricing problem. Four features on the card and one date tell you which cards to check, and a single search tells you whether anybody is buying. Do the sort first and the pricing afterwards, or you will spend an evening looking up cards worth nothing.
Look for a number out of a number
A serial number printed during manufacture states the run. It is the only common case where supply is disclosed rather than inferred, and it is the strongest single reason to check a card individually, whatever the player's name is.
Look for a signature on the card itself
An autograph applied by the manufacturer to the card surface is part of the card and trades as such. One on a clear sticker stuck to the card is worth less to most buyers and the card usually says which it is. An autograph obtained in person is a different market entirely, because the buyer cannot verify it from a photograph.
Look at the date
Anything before about 1980 is worth a look because print runs were smaller and survival was worse. The late 1980s and early 1990s are the opposite case on both counts, which is why those cards stay cheap no matter who is on them.
Then check somebody is buying
One search on completed sales settles it. Five recent sales means a market and a price; none means the card is illiquid, whatever it might theoretically be worth. For most of a box the answer is none, and finding that out in a minute is the point of the routine.
Questions people ask about how to know if baseball cards are worth anything
Do I need to check every card?
No, and you should not. Sort on the four features and the date, check the small pile, and treat the rest as bulk.
What if I inherited a collection and know nothing about cards?
The same sort works. It uses what is printed on the cards rather than knowledge of players, which is exactly why it is written that way.
Should I take them to a shop?
This site does not direct readers to businesses. What it can tell you is that walking in with twenty cards you have already priced is a different conversation from walking in with a box you have not.
Is there a fast way to spot inserts?
They look different from the base cards around them and carry their own set name. If a card stands out in a stack, that is usually why.