Stop here essentially for this merchant (9)
I believe the answer is:
stationer
'this merchant' is the definition.
(stationer is a kind of merchant)
'stop here essentially' is the wordplay.
'stop' becomes 'station' (eg a stop on a train journey).
'essentially' means to look at the middle letters.
The middle of 'here' is 'er'.
'station'+'er'='STATIONER'
'for' is the link.
(Other definitions for stationer that I've seen before include "Seller of paper, pens, etc" , "source of writing materials" , "One assigning position" , "Writing-materials shop" , "I supply rulers: for example" .)