Black market preoccupied by black face (5)
I believe the answer is:
sable
'black face' is the definition.
'sable' can be an answer for 'black' (heraldic term for black). I am not certain of the 'face' bit.
'black market preoccupied' is the wordplay.
I cannot really see how this works, but
'black' could be 'b' (as in pencil classifications) and 'b' is found in the answer.
'market' could be 'sale' (I've seen this in other clues) and 'sale' is present in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
'by' acts as a link.
Can you help me to learn more?
(Other definitions for sable that I've seen before include "fur coat" , "Bales of rich fur" , "Fur from member of weasel family" , "Black; antelope" , "Antelope, fur" .)