The most common and most likely answer to this crossword clue is the 7 plus 2 plus 6 letter word BUREAUX DE CHANGE
B
U
R
E
A
U
X
D
E
C
H
A
N
G
E
Buddy explains!
The straight part
We know that "they convert" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they convert = bureaux de change.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.