Why scams, abuses and everything bad around is not moderated, but the regular members have rights to decide what's wrong and right instead of the forum Staff/Moderators?
Personally, I think allowing the community to sort out community issues is probably the best approach, especially when it comes to subjective cases. Scams aren't always obvious, and it's best to catch a scam before it happens, right? Well, a moderator banning a user just because they seem like a scammer would open a whole can of worms, while if the community does it by applying a flag or trust rating, than trust rating can be openly disputed. If we were to ban those users, the only way to currently appeal a ban his to email admins or appeal in Meta to other staff users. This would likely lead to accusations of corruption, although there's plenty of those accusations thrown around over the years. At least, with the community other community users can disagree in a open way, and sort out who the most suitable users are to judge others, and therefore be included in DefaultTrust, DT2, DT3, and so on.
The forum is full with non-sense, off-topic and spam and no one seems to care about it.
We all care about removing spam, there's moderators actively moderating around the clock to remove it. However, when your moderating a website the size of this forum it can be difficult. Especially, if you have a lot of users posting spam, but not enough suitable candidates for moderators.
If you guys do not know how to moderate a forum, take a look at Sythe, Powerbot, MMORPG and forums that let their Moderators to take actions.
It's not comparable. Do those forums have a eco system similar to Bitcointalk? Signature campaigns are both an advantage, and a disadvantage for the forum. We have our own eco system, but the drawback from that is it does create spam in itself. Bounties don't exist on the forums that you've mentioned, and therefore can't be compared.
Is that how things work like here? Is this some kind of gang-team forum membership where rules and moderation means nothing?
The trust system is far from perfect. However, you could potentially just carry on your day ignoring it. If you use escrow, and guard against the possibility to scam, then it likely won't effect your on forum trading all that much. I don't think anyone will disagree with you here, there's been multiple instances either several forum users gang up, or they are split down the middle, and go to war with each other. That unfortunately is what people do, we can guard against that, but really we can't stop it. This is evident in almost all industries I've been involved in, and worked in.