Crossword Genius

Hard case as a challenge to a beautician (4,8)

Ross

I believe the answer is:

ugly customer

I'm a little stuck... Click here to teach me more about this clue!

'hard case' is the definition.
(I've seen this before)

'a challenge to a beautician' is the wordplay.
I cannot really see how this works, but
'to' is found in the answer.
This explanation may well be incorrect...

'as' is the link.

Can you help me to learn more?

(Other definitions for ugly customer that I've seen before include "Dangerous antagonist" , "Hard case" , "Thug" , "viewed unfairly by shopkeeper?" .)

I've seen this clue in The Globe and Mail.
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