Single transaction that's less than perfect (7)

I believe the answer is:

unideal

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'less than perfect' is the definition.
(I've seen this in another clue)

'single transaction' is the wordplay.
'single' becomes 'uni' (I can't explain this - if you can you should believe this answer much more).
'transaction' becomes 'deal' (a deal is a transaction or exchange).
'uni'+'deal'='UNIDEAL'

'that's' is the link.

Can you help me to learn more?

(Another definition for unideal that I've seen is " Not perfect".)

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

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