Sure, and if this were the only bad coin he'd offered in a string of otherwise good sales, I'd probably be willing to offer some grace. But "I'll pay you $650 to clean up this feedback"... well, I can't help hearing "...because I can't afford to have all the other marks getting scared off".
Ebay's feedback system kind of sucks. When I bought the coin it showed he had 100% positive feedback and when you looked at his feedback page it showed 0 for negative.....but if you clicked the 0 it actually showed he had a few examples of negative feedback for fake coins. I'm not an expert on what he's selling, but he has a few $500-1000 coins from various European/Asian countries that other people in this thread have pointed out look highly suspect.