A card sharp (also card shark, sometimes hyphenated or spelled as a single word) is a person who uses skill and/or deception to win at card games (such as poker). "Sharp" and "shark" spellings have varied over time and by region.
Either works...
Shark likely gained popularity from the existing slang meaning of a ruthless, dangerous person who "preys" on others. The vivid metaphor of a sharp-toothed shark makes sense describing cheaters and hustlers looking for a quick meal in the form of naive players‘ money.