Hello Phil,
With regard to your first paragraph, I merely used your own argument with a logical extension, and I asked you clarify your position with regard to this forum.
As you don't name the other forum where the problem arose, it is difficult to draw meaningful conclusions. The core subject matter could be very different which means the readership will also be different, and they may be generally more or less vulnerable from being taken in. Also each forum has its own rules and methods of policing.
Currently PC does not pre-filter posts on this forum, so it is of course possible for a company or employee to obtain a nickname and make postings. Some companies do make regular contributions, but they are open about who they are, and in 99.9% of cases they avoid blatant advertising, but they do offer constructive advice, and I believe the forum owners are perfectly happy for this.
I am often surprised at how quickly action has been taken, when happening on a thread that has an ominous moderators comment telling us the thread has been removed, and I haven't seen any of it previously. But that is down to our volunteer moderators, and there will be times when a non conforming post is put up, and moderators either aren't on line or don't spot it, so it may remain live for several hours.
I personally believe it would be wrong to stifle praise from customers. And I don't see any justification for such censorship. It is a legitimate expression of satisfaction and it may help other readers to make a better-informed decisions. Unlike complaints, it has no implication for libel as it has no defamatory content.
As for making purchases, as always the buyer has to be aware, and to make sure in their own minds that the products they are considering do what they want, and are at the right price. There are plenty of protections in place for customers provide they deal with regular businesses. Distance selling regulations for mail order, SOGA and contractual cooling off periods, and buyer protection when using credit cards etc.
People with criminal intent will always try to find ways to circumvent curbs to their activities, and websites are no less vulnerable to their attention. A major part of customer protection is the customer responsibility to be "buyer beware". The PC forum as part of its rules does not allow advertising. So if a post is put up that is advertising then the readers know it should not be there, and to treat it with caution.