No, manager cannot always know whether a project will end in a scam but managers should look into whether the developers or the company they work for are as responsible as they should be. In my opinion manager should do their best to find out. For example, a manager should stop a campaign when a red flag is detected, such as plagiarism in a white paper, and ask the project owner for an explanation.
In most cases, managers just do their job. But sometimes things go so badly wrong that the manager has no choice but to close the campaign. I have seen many good managers stop bad projects where the developer has committed serious errors.
It's very important and it should be at the right time once there is an accusation the campaign should be paused and will only continue if the project is cleared of all the allegations, managers should not be too attached to one campaign, that they will defend it whatever the cost, only in house manager will do that, the manager should keep his reputation clean because the campaign managers competitions are very tough and there are only a few good campaigns to manage.