Who you wouldn’t trust to give you a hand? (9)
I believe the answer is:
cardsharp
'hand?' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cardsharp that I've seen before include "Swindler in game" , "Cheater at the table" , "Dodgy dealer" , "cheat" , "Cheater at, say, poker" .)