Market more than 50 lines after public store depleted (7)
I believe the answer is:
outsell
'market more than' is the definition.
(to outsell is to market more than another trader)
'50 lines after public store depleted' is the wordplay.
'50 lines' becomes 'll' (two abbreviations for line. I am not sure about the '50' bit.).
'after' means one lot of letters go next to another.
'public' becomes 'out' (out can mean released to the public).
'depleted' says to hollow out the word (remove centre letters).
'store' with its centre taken out is 'se'.
'out'+'se'='outse'
'll' after 'outse' is 'OUTSELL'.
(Other definitions for outsell that I've seen before include "Retail better than" , "Get more buyers than the competition" , "(Of a commodity) attract more customers than" , "conquer in the market" , "Surpass in sales" .)