The most common and most likely answer to this crossword clue is the 2 plus 8 letter word GO PLATINUM
I've seen this crossword clue in The Guardian
G
O
P
L
A
T
I
N
U
M
More clues leading to the result GO PLATINUM
Buddy explains!
The straight part
We know that "Sell a very large quantity/Sell a very large quantity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sell a very large quantity/sell a very large quantity = go platinum.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.