Sell track again? (6)
I believe the answer is:
retail
This clue is a double definition.
'sell' is the first definition.
(retailing is a kind of selling)
'track again?' is the second definition.
('tail' can be a synonym for 'track' so perhaps 'retail' is OK for 'track again')
(Other definitions for retail that I've seen before include "High street selling" , "Sell (in shop)" , "Sale of goods individually" , "Sell - supply account" , "Form of sales" .)