Competent crew showing polite behaviour (4,7)

I believe the answer is:

good manners

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'polite behaviour' is the definition.
'good manners' can be an answer for 'behaviour' (good manners is a kind of behaviour). I'm not sure about the 'polite' bit.

'competent crew' is the wordplay.
'competent' becomes 'good' (synonyms).
'crew' becomes 'manners' (I can't justify this - if you can you should believe this answer much more).
'good'+'manners'='GOOD MANNERS'

'showing' acts as a link.

Can you help me to learn more?

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

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