The most common and most likely answer to this crossword clue is the 6 letter word MERGER
I've seen this crossword clue in The Sunday Telegraph
M
E
R
G
E
R
More clues leading to the result MERGER
Buddy explains!

The straight part
We know that "business deal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case business deal = merger.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.
What does MERGER mean?
MERGER noun- One that merges.
- The act or process of merging two or more parts into a single unit.
- The legal union of two or more corporations into a single entity, typically assets and liabilities being assumed by the buying party.
- An absorption of one or more estate(s) or contract(s) into one other, all being held by the same owner; of several counts of accusation into one judgement, etc.
- A type of sound change where two or more sounds merge into one.