It is not income of cost institute.
According to me, you don't aspect that your marks will increase more than 1 or 2 marks per paper. If your marks increase 10 or more than 10, that means 1st verification is totally false.
Your mark will be increase up to 3 per paper if you write answer is standard to carry this marks. Many times marks are remain unchanged.
There is no guarantee to increase your marks.
Also there is some uncommon return about this matter.