A deserter seems tip-top to an artist! (3)
I believe the answer is:
rat
'a deserter' is the definition.
(both can mean a traitor)
'tip-top to an artist' is the wordplay.
'tip-top' becomes 't' (top of the word 'tip-').
'to' means one lot of letters go next to another (I've seen this in other clues).
'an artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
't' put after 'ra' is 'RAT'.
'seems' is the link.
(Other definitions for rat that I've seen before include "Treacherous person" , "one escaping doomed vessel?" , "Sewer rodent" , "Destructive rodent" , "Unpopular rodent" .)