I don't know why he should have to do the maths...and it's your maths anyway. I see about 20 numbers in here, so exactly what math are you talking about?
Sellers done the right thing by at least stipulating a price - and even if his ask is a bit of a stretch, so are most prices on here. Worth noting - Chan's sold in just a couple of days. Also, I saw one sell in Tassie in just 2-3 days, not going at all, in a worse condition, with less mods, and in a smaller market, for $6K. Which puts a floor under this price (well, theoretically). So I'd say it's not unreasonable for him to be getting $8-9K, maybe up to $10K for someone who has a block that they've got no use for (some people can't sell the RB26DETT at $3500 either). In which case asking $12K is fair, as I presume he's negotiable anyway.
Give the guy a break.
GJ - for watching yer back - sell it to me for $5K!