There are some simple and some not so simple aspects to this question.
Firstly, Audiogon requires that people register as a "Commercial User" if they fit certain criteria, part of which state:
-You will be buying and selling products for profit on a regular basis.
-You are a reseller or retailer of audio video equipment or related products.
-You represent, or are employed by a manufacturer in the audio video industry.
-You will be listing products on behalf of either of the above entities.
Admittedly, our criteria are based upon the selling/advertising aspects of this site, but they DO apply to forum participation as well. The above criteria seem to cover most users who clearly have "financial interests" in this industry. The examples of users that are being implied in this thread, should in our opinion be registered as commercial users and will be prompted to do so.
However, it is particularly difficult to make the distinction on THIS site, because almost all users will sell something at some point. Some "private" parties buy and sell many items each month, often concentrating on a few brands. For example, let's say Joe has one or two BB amps to sell. He may be motivated to "talk up" that brand, or even tubes in general, hoping to positively influence his sales. Or, Joe might down-play the quality of CC amps, even though he has never owned one. While the ads are online, readers could click on his Username and see that he is selling his BB amps. But after the ad has expired, readers of Joe's "advice" will not be aware that he was selling a BB amp at the time he posted the advice.
Further, the definition of a "dealer" or even "manufacturer" is changing everyday. Until recently, a "dealer" needed to prove the existence of a business entity, provide previous trade references, and have a retail store. But currently, there are many manufacturers who are willing to work with any person that is willing/able to buy some quantity of products. Similarly, "manufacturers" needed to have a large budget to produce, market, and promote products (ads, shows, etc). Currently, there are quite a few companies that market cables for example, over the internet, with little or no budget. The point being: there is no longer a set of hurdles for people to cross from a "private" entity to one with financial interests in a product (directly, indirectly, or despite of). Thus, it is more likely today that people will drift in and out of the commercial status overnight.
In summary, Audiogon DOES require users with financial interests in audio to register as a "Commercial User", and this status is displayed when a forum participant's Username is clicked. However, it is worth keeping in mind that Audiogon is indeed a marketplace, and that EVERY user's advice could be suspect. While we do try to "label" some users as commercial in nature, let us not forget that virtually everyone here will spend money or collect money for audio products - sooner, or later, or earlier.