‘Honesty’ versus ‘Convention’ – what’s the best policy?

I struggled to find the right approach to comment on a social network site recently. I suspect I’m not alone in my dilemma. My problem is I’m not a natural salesperson – getting out there and being pushy, ‘in your face’, doesn’t come easy to me; I’m more a persuader. So I studied a variety of posts across different writing ‘groups’ – here’s what I see.
Now by the way when I use the term ‘convention’, I intend no slur on ‘conventions’ i.e. meetings of like minded folk, businesses etc. No, I’m not thinking of those kind of ‘conventions’, I’m thinking of the ‘convention’ for posts on social networks sites.
The ‘convention’ as I understand it – although I’m new to this so correct me if I’ve got this all wrong – the ‘convention’ is that we post comments/start discussions/follow threads/make contributions to help one another with info, advice, ideas, our experiences, even entertain, provoke controversy etc.in our chosen field – in our case writing. Yet I see a lot of posts, not necessarily on every site (is that down to moderating?), that read.’Look, here’s my book, go buy.’ Now is that just being plain honest or is it not abiding by the ‘convention’. Sure, we all want to promote, sell our writing but hey – is a little more ‘subtlety’ needed, more imagination, to be more interesting or is that not being ‘honest’? The saying used to be ‘Publish and be Damned’. Is it now ‘Promote and be Damned’? I suppose I’m feeling my way into this world of social networking. But surely it isn’t the case that the person who shouts loudest and most often is the one that that gets heard. Or is it?
What do others think?