Some guidelines:
1. Free speech - you can say anything as long as it is relevant and presented in a calm and polite manner. Swearing, SHOUTING etc. make your post more likely to be removed.
2. No zero value posts or threads, like "SELL SELL SELL"
3. No pointless or uninteresting threads.
4. No referral code spam
5. No NSFW content
How is the value of a post evaluated?
This is all about QUALITY. If we want to have posts to qualify to a certain standard, we must have measures for that.
So how we get those measures, who has them?
The answer is: no one, because post's quality measures actually should be an agreement between forum members. In respect of the forum posts, we need:
1) A standard of LOW-NORMAL-GOOD-EXCELLENT quality post.
2) How we define them (measures).
If that quality standard for forum posts is described clearly enough in the forum guidelines, everyone should be able to assess the quality/value of their posts.
And if someone goes against the forum culture, moderators will stop them.
All in all, without clear, but short descriptions of what is acceptable and what is not in forum posts, people continue to wonder, why their posts get removed sometimes.