Top salesman, hardly needed to shift this? (4,6)
I believe the answer is:
best seller
'hardly needed to shift this?' is the definition.
The definition suggests a singular noun which matches the answer.
'top salesman' is the wordplay.
'top' becomes 'best' ('best' can be similar in meaning to 'top').
'salesman' becomes 'seller'.
'best'+'seller'='BEST SELLER'
(Other definitions for best seller that I've seen before include "What many people are buying" , "Popular book" , "Book bought by many" , "Book bought in large numbers" , "Blockbuster" .)