Amazing reductions at start of day, but not one for DIYers? (5,8)

I believe the answer is:

trade discount

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'not one for diyers?' is the definition.
I can't judge whether this defines the answer.

'amazing reductions at start of day' is the wordplay.
'amazing' is an anagram indicator.
'start of' suggests taking the first letters.
The first letter of 'day' is 'd'.
'reductions'+'at'+'d'='reductionsatd'
'reductionsatd' is an anagram of 'TRADE DISCOUNT'.

'but' is the link.

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I've seen this clue in The Times.

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