Limit leading posters for despicable sorts (5)
I believe the answer is:
toads
'despicable sorts' is the definition.
(toad can mean a despicable person)
'limit leading posters' is the wordplay.
'limit' means to remove the last letter (the word is limited or incomplete).
'leading' becomes 'top' (both can mean first-class).
'posters' becomes 'ads' (poster is a type of advertisement).
'top' with its final letter taken away is 'to'.
'to'+'ads'='TOADS'
'for' is the link.
(Other definitions for toads that I've seen before include "Leaping amphibians" , "Loathsome types" , "Froglike amphibians" , "Frog-like land animals" , "Tailless amphibians" .)