i would say its a
small carp, in that your info is more help to buyers than the seller
it is up to the buyer to research what they are buying/ask questions of the seller
unsolicited input that reduces the number of potential buyers, be they informed or non-informed isn't helping him sell his item
if he isn't trying to sell broken stuff, i don't think the seller has to point out every flaw/downside of an item, you don't see advertisements listing all the bad things about a product, do you?
if the seller is smart he will drop the whole thing, let the thread fall away (which it will do quickly in for sale/trade) and then repost it in a few days, or even just go sell it on another forum
just my newbie trader $0.01
*EDIT*
i just noticed he took
9 days to respond to vipers post, that was DUMB, he should have let it go and started a new thread instead of posting to it and pointing out the whole thing in public, dumb move by that dude, not a good way to sell things