Be wary of master, all's not right (5,1,3)

I believe the answer is:

smell a rat

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'be wary' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'master all's not right' is the wordplay.
'not right' indicates an anagram.
'master'+'all'='masterall'
'masterall' anagrammed gives 'SMELL A RAT'.

'of' acts as a link.

Can you help me to learn more?

(Other definitions for smell a rat that I've seen before include "Sense something suspicious" , "Suspect deception" , "Detect something suspicious" , "Suspect trickery (colloq.)" , "Find something fishy" .)

I've seen this clue in the Sydney Morning Herald.

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