Trio arranged composition that's selling really well (7,5)

I believe the answer is:

roaring trade

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'selling really well' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'trio arranged composition' is the wordplay.
'composition' indicates anagramming the letters.
'trio'+'arranged'='trioarranged'
'trioarranged' with letters rearranged gives 'ROARING TRADE'.

'that's' is the link.

Can you help me to learn more?

(Another definition for roaring trade that I've seen is " delights the shopkeeper?".)

I've seen this clue in The Irish Times.

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