Do you only have to pay it if you lose? (6,3)

I believe the answer is:

search fee

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'it if you lose?' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'do you only have to pay' is the wordplay.
'do you only' becomes 'search' (I can't justify this - if you can you should believe this answer much more).
'have' is a charade indicator (letters next to each other).
'to pay' becomes 'fee'.
'search'+'fee'='SEARCH FEE'

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I've seen this clue in the Evening Standard.

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