It sucks that it has some paint damage but honestly, I think the top will sell for pretty close to his asking price. the lowest would be around $700. Not everyone is looking for a pristine condition top. I live in Chicago and purchased a hard top for the brutal Chicago winters. I didnt really care what the condition of the paint was since it would probably be under a few inches of snow most of the time. I also wanted the larger glass rear window and defog. life saver when it is 10 below zero
others may just want the hard top to participate in autocross events so dont care about aesthetics.
You can offer $500 or less but the seller will most likely decline. You are also competing against potential buyers that either have painting capabilities or can have it done really cheap so they would not value the repair at $450.
It comes down to how bad you want a hard top. Hard tops in my area pop up once every 6 months and go quickly.