The most common and most likely answer to this crossword clue is the 7 letter word HAGGLED
I've seen this crossword clue in The Guardian
H
A
G
G
L
E
D
Buddy explains!

The straight part
We know that "Negotiated" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case negotiated = haggled.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 HAGGLED mean?
HAGGLED verb- To argue for a better deal, especially over prices with a seller.
- To hack (cut crudely)
- To stick at small matters; to chaffer; to higgle.