Concern about profits almost entirely seen in marketplace? (3,4,4)
I believe the answer is:
car boot sale
'profits almost entirely seen in marketplace?' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'concern about' is the wordplay.
I cannot quite see how this works, but
'about' could be 'ca' (abbreviation for 'circa') and 'ca' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for car boot sale that I've seen before include "Where unwanted possessions may be disposed of" , "Vending of second-hand goods from private vehicles" , "Event involving trade conducted from the back of one's vehicle" , "field event?" , "Where you'll see many a bumper" .)