Finish with us and the final right customer (3,4)
I believe the answer is:
end user
'customer' is the definition.
(I've seen this before)
'finish with us and the final right' is the wordplay.
'finish with' becomes 'end' (synonyms. I am not sure about the 'with' bit.).
'and' means one lot of letters go next to another.
'final' says to take the final letters.
'right' becomes 'r' (common abbreviation).
The final letter of 'the' is 'e'.
'end'+'us'+'e'+'r'='END-USER'
Can you help me to learn more?
(Other definitions for end user that I've seen before include "Person for whom a product is destined" , "Ensured (anag.)" , "Ultimate recipient of goods" , "One getting the ultimate enjoyment" , "Final recipient of product" .)