Try one's level best to swindle as many as possible (2,3,3,3)
I believe the answer is:
do all one can
'try' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'one's level best to swindle as many as possible' is the wordplay.
I cannot really see how this works, but
'level' could be 'o' (O level is an example) and 'o' is found in the answer.
'best' could be 'a' and 'a' is found in the answer.
'many' could be 'l' and 'l' is present in the answer.
'possible' could be 'on' ('not on' can mean unacceptable or not possible) and 'on' is found in the answer.
'one' could be 'an' (I've seen this in other clues) and 'an' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for do all one can that I've seen is " Try one's hardest".)