Gain a percentage but is appealing (7)
I believe the answer is:
winsome
'is appealing' is the definition.
(I've seen this before)
'gain a percentage' is the wordplay.
'gain' becomes 'win' (synonyms).
'a percentage' becomes 'some' (I've seen this in another clue).
'win'+'some'='WINSOME'
'but' acts as a link.
(Other definitions for winsome that I've seen before include "Charming (in a childlike way?)" , "Attractive and fresh" , "Holding an appeal" , "Pleasant" , "Agreeable" .)