1. I stormed on some companies sponsoring campaigns whereby the Campaign manager is red trusted, almost all the participants of the campaign are red trusted. The company tried to open some sort of honest review by users. Yet, the review was influenced with money.
Even under the review, some users were crying how they were defrauded by same company.
It is clear to me which campaign is in question, but you must know that scam as such is not moderated on this forum - which means that forum members can act in accordance with their beliefs through trust and flags system and thus warn others of something bad. It is up to each individual to assess the situation and do what they think is right - of course some people do everything for money in real life, hiding behind an online identity makes things even easier for them.
2. Amidst this, people are still patronizing the company. Does it therefore mean that the red flag or trust is not the true representation of a user. Can a user be a saint and yet red trusted by many?
You have users who have 50+ positive trusts, and 5+ negative ones - whether someone calls them saints or devils is completely irrelevant. If you personally trust someone, then it doesn't matter how many negative trusts there are, does it?
3. These campaigns pay good money. Where exactly does this money come from? From the defrauded individuals or the company generated profits?
Maybe from the source you mention, and maybe most of those who participate in the said campaign are not actually unique users but alt accounts of that same company. In other words, perhaps the company pays most of the money to itself - because the pay rate definitely raises the suspicion that there are some strange things besides the obvious ones.
4. Even if the forum cannot or does not want to do anything about scam moderation due to certain reasons, is there no a specific amount of red trust a user should get without a corresponding positive trust and get banned?
As far as I know the answer is no, no one will be completely banned just because they get a certain number of negative feedbacks.
5. A user who in past associated with scam and on the long run sincerely repents, is there a way the red trusts can be reversed, or is it as irreversible as the merit?
Feedback can be removed instantly from the one who left it at any time, and it happens every day - people change their minds, delete or change feedbacks - it's not something permanent like merit, although admin has the ability to intervene in case of merit abuse.