Are you just complaining because you have bought something you now don't need? It is eBay, it is a used part off a race car. If you were after a new one with no dents, perhaps a new one should of been bought. I'm not defending the seller, but I think you need to realise what you are buying and where from, the clues are all there in the description. Had it said new and unused and you paid a lot of money for it yes, I could see your frustration. Someone has offered to take it from you so accept an offer, move on and next time check what you are buying. Cruel I know but, sometimes it is the way.
Your first point no not at all I messaged the seller straight away thinking it had been damaged in transit. I then got a reply saying they did it whilst removing the manifold. I do think I am within my rights because they have hidden the dents in the photo and also they didn't mention it. If you were selling a 90,000 mile car you'd expect dents and scratched to be mentioned this has no mention of wear whatsoever. Since buying it I have changed my mind but in no way does that impact my decision with the seller. I am happy to sell it and move on just think that the dents should have been mentioned because if I was selling it I would mention