I can only assume this guy is a member of this forum.
Actually, I think it's pretty unlikely it was a member. You'd be surprised how many Klassic K owners don't know about this forum, plus, I think all of us here whatever our opinion on 'builds' is, are pretty desensitized to the practice since there are so many people doing it.
You're also underestimating how many old-school BMW riders are old, white, know-it-all, calcified douchebags. So many are, that I think you may have wasted some of your own valuable time gracing that particular douchebag's mailbox with a response.
He's right, though -- these bikes aren't rare at all. When you say there are 'only' 5 on eBay, that's actually a lot. Three years ago you wouldn't see any K-bikes on eBay. The fact that there are so many means the supply is outstripping the demand. I suspect people who want a cafe K-bike don't want a ready-made one by someone else, they want bragging rights for having done it themselves.
Maybe this is a cautionary tale for K-bike cafe builders everywhere wrt resale value and overall demand on the market.
No ill will intended -- seriously, I hope it sells and I hope you get the price you want.