The most common and most likely answer to this crossword clue is the 4 letter word AGIO
I've seen this crossword clue in The Guardian
A
G
I
O
More clues leading to the result AGIO
- In days gone by, I pocketed commission
- . . . . what would you give to exchange something precious with me?
- Exchange fee one’s invested in in the past
- Charge to exchange silver I owe, I’m told
- Initially accept good Indian offer of money exchange fee
- A soldier getting nothing as a fee
- d Money-changing villain suffers current depreciation?
Buddy explains!

The straight part
We know that "commission" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case commission = agio.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 AGIO mean?
AGIO noun- The premium or percentage on a better sort of money when it is given in exchange for an inferior sort. The premium or discount on foreign bills of exchange is sometimes called agio.