[Mr70]

I think he should refund your full price paid,including shipping costs,regardless of who's at fault,if anyone even is.
Have you tried calling him on the telephone,or talk to him in person?
You might find him more lenient once you do.
In this day & age of the anonymous internet,a lot hide behind the Keyboard,and don't think it will go any farther then that.
If I sell something via the internet,I always contact the buyer once I know they took possesion,and ask them Flat out,"ARE YOU HAPPY WITH IT?"
If it's a reputable part,in reputable condition,& you're both reputable people,it should be amicable.