The most common and most likely answer to this crossword clue is the 13 letter word PART-EXCHANGE
I've seen this crossword clue in Financial Times
P
A
R
T
-
E
X
C
H
A
N
G
E
Buddy explains!

The straight part
We know that "Deal/ involving organ transplant?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case deal/ involving organ transplant? = part-exchange.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 PART-EXCHANGE mean?
PART-EXCHANGE verb- To supply (an item of goods), along with money, in exchange for other goods or services.