Official worth employing? That can be denied (9)

I believe the answer is:

refusable

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'employing? that can be denied' is the definition.
I can't tell whether this defines the answer.

'official worth' is the wordplay.
'official' becomes 'ref' (match official in football, say).
'worth' becomes 'usable' (I can't explain this - if you can you should give a lot more credence to this answer).
'ref'+'usable'='REFUSABLE'

Can you help me to learn more?

(Another definition for refusable that I've seen is " not compulsory".)

I've seen this clue in The Independent.

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