Dan - That raises the question of how can you tell who has an interest and who doesn't? We're back at square one where this thread opened. Even if we have a precise definition (not trying to sell speakers) for what we think a shill is, there remains the problem of deciphering the intent and appropriateness of what we read in a forum.
Say someone who worked for Nottingham* came into the forum and started posting anonymously about how great Nottingham* turntables are. We would all probably agree that Nottingham does makes really good TT's, but the employee is still a shill, because he (or she) isn't disclosing they they have an interest in seeing more Nottingham products sold.
OTOH, I don't work for Nottingham*, I don't know anyone who does, I don't own a piece of the company, etc., I just like the turntables they make and I write lots of posts raving about how I love my Nottingham TT and recommending it to everyone. Unless you know me personally, how can you, or anyone else, tell the difference between me and the shill?
The answer is that you can't. You have to make a judgment call, based on your knowledge of me, the (possible) shill poster, our relative past posting history, the product and company, etc. Which is absolutely no different from virtually everything else, especially on-line. You're never absolutely certain, even if it's from someone you have agreed with in the past. And your own experiences aren't going to help much, because even if the product they are pushing is something you are also raving about, they are still shilling if they have a vested interest.
(*Nottingham is used strictly as an example, in no way am I implying that Nottingham does or ever has used shills.)