Posh sort of business (4)
I believe the answer is:
shop
'business' is the definition.
(I know this)
'posh sort' is the wordplay.
'sort' indicates an anagram.
'posh' with letters rearranged gives 'SHOP'.
'of' acts as a link.
(Other definitions for shop that I've seen before include "Sell" , "Store - betray" , "place of work" , "Establishment for the sale of goods" , "Retail outlet" .)