At the trading centre, the charge for a meal (4)
I believe the answer is:
feed
'a meal' is the definition.
(I've seen this in other clues)
'at the trading centre the charge' is the wordplay.
'at' means one lot of letters go next to another.
'centre' indicates the central letters.
'the charge' becomes 'fee' (fee is a kind of charge).
The middle of 'trading' is 'd'.
'd' put after 'fee' is 'FEED'.
'for' acts as a link.
(Other definitions for feed that I've seen before include "Provide food" , "Given payment" , "Give (or take) nourishment" , "Paid" , "take grub" .)