Commission from unsuitable agent - creep! (10)
I believe the answer is:
percentage
'commission' is the definition.
(I've seen this before)
'unsuitable agent creep' is the wordplay.
'unsuitable' indicates an anagram (letters not in suitable order).
'agent'+'creep'='agentcreep'
'agentcreep' anagrammed gives 'PERCENTAGE'.
'from' is the link.
(Other definitions for percentage that I've seen before include "Proportion in each 100" , "Proportion, share" , "Proportion stated in hundredth parts" , "cut?" , "Maybe commission" .)