That's why pins on eBay are listed for 2x to 3x their normal selling price, because eBay is a huge hassle to deal with. Wait until you ship the machine and he files a dispute with PayPal. Your money will be tied up for months. There are way more efficient ways to sell locally if your price is on point.
As for your situation, keep trying to contact eBay. I had a user harassing me on there a couple years ago, and they were very decent to deal with once I got through.