Tell niece, working, to see customers (9)
I believe the answer is:
clientele
'customers' is the definition.
(I've seen this before)
'tell niece working' is the wordplay.
'working' indicates an anagram.
'tell'+'niece'='tellniece'
'tellniece' with letters rearranged gives 'CLIENTELE'.
'to see' is the link.
(Other definitions for clientele that I've seen before include "Market" , "Customers of a business" , "A shop's customers" , "Clients collectively" , "customers round" .)