How much are basketball cards worth depends on two things more than in any other sport: which rung of the parallel ladder you are holding, and how recently your comparables sold. Get those two right and the arithmetic is the same as anywhere else.
The rung decides the order of magnitude
A base card and a low-numbered parallel of the same player, from the same set, with the same photograph, sit in completely different price brackets. The distinguishing feature is often a border colour or a foil treatment. Establish which you have before searching, because the search will otherwise answer a question about a different card.
Recency decides the rest
Basketball prices respond to performance within days, so comparables age faster here than in baseball. Keep your five sales inside a few months, and inside a few weeks for a player having an unusual run. A sale from last season is evidence about last season.
Where the older value sits
1980s rookies and the scarce inserts of the 1990s carry most of basketball's pre-modern value. Base cards from the overproduced years are common and priced accordingly, which is the answer for the bulk of most boxes from that period.
Then run the numbers
Five sales into the card value checker gives the middle-three figure, the mean beside it and the spread. Add your marketplace's percentage and postage to see what you would keep. On lower-value basketball cards those two together often take more than a third of the price.
Questions people ask about how much are basketball cards worth
Why is my card worth so much less than one I saw sold?
Check the parallel first. In basketball that is the explanation far more often than condition or timing.
Do prices drop when a player retires?
Sometimes, sometimes not, and not predictably. Read recent sales rather than reasoning about it.
Are autographed basketball cards worth more?
Manufacturer autographs generally are, and how much depends on the player and the scarcity of that particular card. Sticker and on-card autographs are priced differently by buyers.
What is a reasonable condition assumption?
Assume yours is one grade worse than you think. That habit costs nothing and prevents most disappointments.