This reminds of a post I made a while back called Bloggers versus Political Bloggers where Political Bloggers seem to get away with a lot more than what I've seen around the marketing blog world. In my two years of actually working in the political world, I've seen posts made that were based on no facts and when pointed out to that, the author just ignored the comments. I've seen well known columnists shill for a politician and create negative comments about their competition. Add to that the brew ha with over zealous commenting bots and pay for comments and you can see that it really is a wide open range for what is acceptable and not acceptable.
From the corporate marketing world pay per posts are frowned upon. Making obviously fake posts and websites (like WalMart flogs) are quickly discovered and reported on. Shilling for a corporation or product is considered unethical unless you properly disclose it. Marshalling tactics like some of those mentioned in the YouTube post above are not kosher; why else would Dan refuse to name clients of his that participated in these schemes.
As with any reporting or writing you really need to understand the motivations behind the author. Whether it is to make money, retire early, support a candidate, or whatever it really matters to understand what the blogger's storey is (mistake on purpose). Besides figuring that out, your best bet is to get multiple views on a subject that interests you and that includes main stream media. Personally I've found that the "truth" is always somewhere in between the different views and who knows you might learn something new in the process when you listen to an opposing view point.