The most common and most likely answer to this crossword clue is the 4 letter word VEND
I've seen this crossword clue in The Times
V
E
N
D
Buddy explains!

The straight part
We know that "market" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case market = vend.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 VEND mean?
VEND noun- The act of vending or selling; a sale.
- The total sales of coal from a colliery.
- To hawk or to peddle merchandise.
- To sell wares through a vending machine.
- The letter Ꝩ/ꝩ, used in Old Norse, related to the rune wynn (ᚹ, whence also Latin-script Ƿ/ƿ) but with the bowl open at the top, like a y.