A sitter, maybe, but not all that easy (5)
I believe the answer is:
poser
'a sitter maybe' is the definition.
(I know that art model is a type of poser)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for poser that I've seen before include "Spore raises a difficult question" , "Attitudiniser" , "A puzzle made of ropes" , "Hard question" , "This person's affected" .)