Quite a good likelihood it's on the up and up? (4,6)

I believe the answer is:

fair chance

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'quite a good' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'likelihood it's on the up and up?' is the wordplay.
'likelihood' becomes 'chance' (I've seen this before).
'it's on' says to put letters next to each other (some letters go on the end of others).
'the up and up?' becomes 'fair' (I can't justify this - if you can you should give a lot more credence to this answer).
'chance' put after 'fair' is 'FAIR CHANCE'.

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I've seen this clue in the Evening Standard.

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