The linked article is 10 years old, and the situation on ground has changed a lot, specifically due to concentrated efforts by the central government to prevent tax evasion. I'm not aware of the figures, and a majority chunk of income-earners still doesn't pay income tax, but it's most definitely much less than the 97% that you mentioned.
Tax evasion as I know it, and as has been informed to me by many financial consultants I've talked to, is now increasingly difficult. You really need to have back-channel contacts with the right people and spectacular know-how of the loopholes to pull it off. I'm talking about large-scale evasion here, but much of it stands true for small-scale as well.
