Expert in image-making maybe who walks nervously up and down? (5)
I believe the answer is:
pacer
'who walks nervously up and down?' is the definition.
(someone pacing up and down)
'expert in image-making' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'in' indicates putting letters inside.
'image-making' becomes 'PR' (public relations).
'ace' put into 'pr' is 'PACER'.
'maybe' is the link.
(Other definitions for pacer that I've seen before include "setting the rate" , "Horse; one setting speed" , "walker?" , "Racehorse" , "One setting race speed" .)