How obvious it is the fortune-teller’s a fake? (7,5)

I believe the answer is:

crystal clear

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'how obvious' is the definition.
'crystal clear' can be an answer for 'obvious' (I've seen this before). I'm not certain of the 'how' bit.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for crystal clear that I've seen before include "very plain" , "Incontrovertible" , "That's readily understood" , "Pellucid" , "obvious" .)

I've seen this clue in the Evening Standard.

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