A purchaser is said to have an Arab garment (5)
I believe the answer is:
abaya
'a purchaser is said to have an arab' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'garment' is the wordplay.
I cannot really see how this works, but
'garment' could be 'aba' (aba is a kind of garment) and 'aba' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for abaya that I've seen before include "Clothing for Arab" , "hairy covering" .)