D'Artagnan, for instance, could talk a lot and fool people (6)

'd'artagnan for instance' is the definition.
I can't tell whether this defines the answer.

'talk a lot and fool people' is the wordplay.
'talk a lot' becomes 'gas' (gas can mean to talk at length).
'and' is a charade indicator (letters next to each other).
'fool people' becomes 'con' (I can't explain this - if you can you should believe this answer much more).
'gas'+'con'='GASCON'

'could' is the link.

Can you help me to learn more?