Valuation of site made by partner (8)
I believe the answer is:
estimate
'valuation' is the definition.
(I've seen this before)
'site made by partner' is the wordplay.
'made' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'partner' becomes 'mate' (synonyms).
'site' anagrammed gives 'esti'.
'esti'+'mate'='ESTIMATE'
'of' acts as a link.
(Other definitions for estimate that I've seen before include "Guess, rough calculation" , "damage" , "Reckon, judge" , "Make an educated guess" , "Calculate approximately" .)