Forum rules don't forbid scamming either. Trust ratings are not for enforcing forum rules. Forum rules are enforced by moderators. Trust ratings are for some of the things that are not directly covered by the rules, such as scams, attempts to scam, successful trades, not so successful trades, etc. And yes, that might include deceptive sockpuppeting if it creates a risk to other users.

I don't know where you got that definition but alt accounts can be used for anything. As long as you don't cheat or scam or troll or evade a ban etc - you should be fine. Your colleagues from the Turkish board got caught cheating. "Expressing themselves" wouldn't have involved cheating bounties, vouching for themselves, etc.

Çoklu Üyelik Kullanımı
Forumda çoklu üyelik kullanımı ile ilgili bir sınırlama bulunmuyor. Aksine kendinizi daha rahat ifade edeceğinizi düşünüyorsanız yeni hesap açarak ana hesabınızdan bağımsız şekilde yazmanız teşvik edilir. Burada unutmamanız gereken nokta bir hesabınız banlanırsa hiçbir hesabınızı ceza süresi boyunca kullanamayacağınızdır. Ban üyeliğe değil, kişiye veriliyor.

Multiple Membership Usage
There is no restriction on the use of multiple memberships in the forum. On the contrary, if you think you can express yourself more easily, you are encouraged to open a new account and write independently from your main account. The point to remember is that if an account is banned, you will not be able to use any of your accounts during the penalty period. Ban is given to the person, not membership.