There's nothing illegal about posting up a sales list, events etc, particularly when there are appropriate section on a forum to do so. Although only ever posting 3 times in order to sell one L.P. might be considered as taking the piss
There is always a "honeymoon" period where people post and reply to anything and everything until they get bored, a bit like bidding on ebay!
On most forums there is a spectrum of contributors; on one hand there are people who know each other both socially, (niters, soul nights etc) and through the forum, as a meeting place. On the other hand there are 'anoraks' who know the most bizarre details on the subject. In both cases the "newbie" could feel quite intimidated and may only put their head above the parapet once before being shot down and then shrinking into their shell. If you've stumbled across northern and heard Judy Street but on making an inquiry get the piss ripped out of you, you are not very likely to venture back.
Topics on forums tend to be pretty easy to reply to with a monosyllable and that make it very hard to keep a thread moving forward and hence the input dies off - Do you like sprouts? No, end of story!
Feedback, now here's the rub! Take a look through a forum and see what feedback is given - F*** all in most cases (God knows why Mike bothers!) Take a look at the "comments" next to articles, photos and sound submitted, to say it was minimal would be an over statement! Commitment and enthusiasm wane very quickly with out any constructive or appreciative input