Genuine attic finds would not come on here and post a for sale thread. They most likely would seek valuation as we've seen many many times. Altho they are often funny and deluded, they don't annoy me. I, like you, quite enjoy seeing what people have unearthed and why shouldn't they seek help in finding out what they have.
I think what we're talking about here is installing a system that keeps a little decorum on the forum. Catchy.
Some days it's a little like a hotmail inbox with the junk filter turned off and i've now got to the point where i don't actually open up the "ebay listings" thread and i am always hesitant to open the "for sale" thread as 9 times out of 10 it's not a "proper" in forum sale just links or tat or whatever. I think it's a shame is all and would prefer it if selling here was more of a privilege earned. I think that's a gentle rule that that actually works towards creating a more positive environment. Not a more hostile one. Unlike hurling abuse at all and sundry, which, altho funny, can sometimes that can be misdirected.
I'm not talking about making the forum as a whole elitist, snobby or cold shoulder-ish. I'd hate that. Everything else is a free for all.
I think the only reason not to install some sort of system is if the majority of members enjoy first time/one time sale posts. Cos it's not gonna frighten off any genuine new members, just time wasters.
An after thought: One trend i have noticed is those members who do only come on here to sell (either once or a few times) tend to be pricks. A seller recently came on and posted a sale which i was foolish enough to PM about, wanting 1 or 2 of his figures he was flogging. A few other members did the same. A week went by and i sent a couple of follow up messages but was again ignored. Turned out a couple of other members had the same treatment. Maybe he'd been killed... no such luck. Turned out he had replied to 1 or 2 members and completed sales and altho other members had enquired first, they were ignored. The followed rants by me, one other member joined in... etc etc
I just don't think this sort of thing would go on if the seller was an actual forum member with some history and some pre(to sale)-dialogue etc.