Supplier is very up or miserable (8)
I believe the answer is:
purveyor
'supplier' is the definition.
(purveyor is a kind of supplier)
'very up or miserable' is the wordplay.
'very up or' anagrams to 'PURVEYOR'.
Though, I am not sure how this is indicated.
'is' is the link.
Can you help me to learn more?
(Other definitions for purveyor that I've seen before include "Provider (of goods)" , "Supplier of victuals" , "Retailer" , "Supplier (of food, etc)" , "Supplier of provisions" .)