Does your friend work in real estate or infra company?
As far as bribes are concerned, Project Manager (PM) will not be a fool to ask for his cut on phone. Everyone knows that call-recording Apps are available free of cost and his call could get recorded. These things are discussed separately and not even in office.
Contractors deal with whole lot of PMs. In this industry, many persons have their hands deep in jam of corruption. If the contractor has given complaint then possibly he is yet to learn the tricks of his business.
By reading between the lines, I find two possibilities from your post. First one is about the excess percentage that Project Manager (PM) could be demanding and contractor may not be fulfil this excess demand. The second possibility is that the PM could be tough on quality issues. He might have told contractor to do rework at multiple places. This rework might have eroded contractor's profit. Now to settle score, he might have made a complaint against the PM. Tarnishing image of the PM could be one of the ways of taking revenge. Of course, as stated earlier, this is my hypothesis and it may be true or may not be true.
Why contractor did not understand a simple thing that while making complaint, one has to keep ready the evidence? How can he make complaint without evidence?
One of the lines of your post says, "Now, the challenge is, he want to change his employee mindset rather than removing from the company." Who is he? Do you mean employer? If PM is involved in corruption, then how employer can wait for the change of mindset? What is this quixotic decision? It is beyond common man's understanding. For further queries, feel free to contact me
Thanks, Dinesh Divekar 13th June 2017 From India, Bangalore