Top salesman's first with consumer (7)
I believe the answer is:
sweater
'top' is the definition.
(I've seen this before)
'salesman's first with consumer' is the wordplay.
'salesman's first' becomes 'sw' (I am not sure about this - if you are sure you should believe this answer much more).
'with' says to put letters next to each other.
'consumer' becomes 'eater' (eater is a kind of consumer).
'sw'+'eater'='SWEATER'
Can you help me to learn more?
(Other definitions for sweater that I've seen before include "Knitted upper garment" , "A present from Mum!" , "Jersey may become" , "Top" , "person in a sauna?" .)