Would you help this eBay buyer?

[BernDog]

I wouldn't even go so far as to worry about moral grounds. Sounds like a scam to me. Hells no. If you invoice for $400 and he pays 400, it's his. Don't put yourself out there. Report it. Always keep yourself kosher under ebay's protections. Vary from the norm, and they won't have your back any more.