Two men; one customer (6)
I believe the answer is:
patron
'one customer' is the definition.
(a customer of a business or service)
'two men' is the wordplay.
'two men' means two replacements for 'man'.
'man' becomes 'pat' ().
'man' becomes 'ron' (man's name).
'pat'+'ron'='PATRON'
(Other definitions for patron that I've seen before include "Regular customer or sponsor" , "Financial supporter - customer" , "Pot ran out for protector" , "manager (13) [FRENCH]" , "Saint" .)