Cheat is eccentric and alert (9)
I believe the answer is:
cardsharp
'cheat' is the definition.
(I know that cardsharp is a type of chiseler)
'eccentric and alert' is the wordplay.
'eccentric' becomes 'card' (card can mean an eccentric person).
'and' means one lot of letters go next to another.
'alert' becomes 'sharp' (synonyms).
'card'+'sharp'='CARDSHARP'
'is' is the link.
(Other definitions for cardsharp that I've seen before include "Dodgy dealer" , "Cheater at, say, poker" , "Cheater at, eg, poker" , "Swindler in game" , "cheat" .)