No, I mean, his account has negative trusts, might also get more negative trusts in near future
If he sold his account already he probably managed to do it before receiving red tags. If he hasn't yet but he's trying to, it may be more difficult now, but not impossible. After all, it's still fifth most merited account from the forum. A buyer knowing how forum works would realize that this account is still valuable for making money.
in the best case, might get banned too but I don't have that expectation
I don't think he would be banned now, if he wasn't banned already for well documented and proven plagiarism...
By the way, every signature campaign states that if user has negative trust from DT members, that user won't be able to enroll in signature campaign and that's why I asked, what's the point of buying an account that has negative trust and other issues?
Not all campaigns state that. Look at digaran which, until recently, he was enrolled in a campaign while wearing 7 red tags from DT users. It's only up to the manager. If he will consider those feedbacks as irrelevant he can enroll anyone. And I am sure there would be managers interested in having Ratimov enrolled, even with 2 negative feedbacks.
If no one cares about trust, then what's the point of pointing it out in thread that users shouldn't have negative trust? Or why did Royse thought his negative trust was okay, I can't understand 
As I stated above, not all campaigns have this rule. About what's the point of leaving feedbacks: it's for the sake of users which may be tempted to make deals with these accounts -- by reading those feedbacks they may avoid being scammed. Last, but not least, about Royse: Royse is a perfect example of how a campaign manager should not act. Winning the Antihero "award" at BCA 2022 was no coincidence. If enrolling digaran, which has 7 red tags is not enough proof, you may read here some more about Royse. He actually tends to act like Ratimov in some parts, lol.