It's not often models get flustered! (6)

I believe the answer is:

seldom

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

'it's not often' is the definition.
('seldom' is the opposite to 'often')

'models get flustered' is the wordplay.
'models' can be anagrammed to 'SELDOM'.
Though, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for seldom that I've seen before include "Once in a blue moon" , "Only occasionally" , "Not 21" , "on rare occasions" , "Alluvium" .)

I've seen this clue in the Evening Standard.

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