What should I do?

I bought a part from a member here, and paid what I thought was a fair price. I got the part and its not what was advertised and it is rusted to the point of not being a useable part for me. I got it over a month ago and sent a message to the seller about the part not being what is was supposed the be and of the rust condition. He told me he would make it right. I didn't hear anything for a month so I messaged him. He said he had more than one of these so I asked about the condition of the other parts and he said he would send pics of the other one,that was a week ago and I don't have pics. I paid about twice what I would have if this was a usable because of the way its was represented in the ad. I paid PayPal friends and family to save him the fees so I probably have nothing there to file a claim. I don't know if I waited long enough to name names or not. I see he has more parts he is selling and I don't want someone else to get screwed out of their money. I lost 500.00 out of my car budget with this guy. I have bought a lot of parts here for my car and all have been really good transactions. Buyer beware.
I'm not saying this is 'right', but here's what I'd do. Keep in mind that a used part can be perceived differently as to condition. Pictures sure help, but even then a buyer may be disappointed with the condition when it arrives. I know neither of you, so you could be just a complainer or he could be a liar & we're hearing only one (your) sid4e of the story.
Contact him again (you could even show him your correspondences here), and give him one week to send you a picture of the replacement he has offered. If it looks acceptable, give him a week to ship it to you. If that happened, your problem would be resolved about as well as you could expect. In that correspondence, advise him that, if this IS NOT resolved to your satisfaction (maybe he'd offer a price adjustment or ???) or if he doesn't reply at all, you will post his information on FABO (assuming FABO allows it). Thankfully, I've never had a transaction go that far wrong. I believe years ago a buyer contacted me & was unhappy with the condition of a part. I told him I'd adjust the price to his satisfaction. He gave me a 'number' and that's what I did - even though (IMHO) I thought the original price was fair. The $20 or $30 wasn't as important as having a satisfied buyer. I haven't done that many parts over the years, but I've been on both 'sides'. The vast majority of those transactions were quite friendly - as are most MOPAR guys.