The most common and most likely answer to this crossword clue is the 6 plus 8 letter word MONKEY BUSINESS
I've seen this crossword clue in The Guardian
M
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More clues leading to the result MONKEY BUSINESS
- Company after £500 in shady deal
- Fiddling finance firm pocketing a grand
- Mischief as a result of cocktail served during 1 down 22’s work
- £500 and I’ll do it!
- Mischief aboard vital vehicle popular during disorder
- Hanky-panky king breaking bank, say?
- Wicked kinsmen use boys for making mischief
- King moves into cash trade involving shady dealing
- Dirty tricks investing thousand in finance company
- Misbehaviour of king in banking, for example
Buddy explains!
The straight part
We know that "shady dealing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shady dealing = monkey business.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.