Wickedly appealing for a merchant’s bonus (9)

I believe the answer is:

lagniappe

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'merchant's bonus' is the definition.
'lagniappe' can be an answer for 'bonus' (thesaurus). I'm unsure of the 'merchant's' bit.

'wickedly appealing' is the wordplay.
'wickedly' is an anagram indicator (I've seen this in other clues).
'appealing' with letters rearranged gives 'LAGNIAPPE'.

'for a' acts as a link.

Can you help me to learn more?

(Other definitions for lagniappe that I've seen before include "small donation" , "present" , "Gratuity" , "tip" .)

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

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