There are many ways deployed by tax authorities to catch tax evasion offenders. The agencies look into social media footprints, take the help of whistleblowers, computer data analysis, etc. You can read about the Black Money, Tax-Evasion & Tax-Avoidance in the given link.
Currently financial institutions and banks share information about very high value withdrawals, deposits, purchase of immovable properties, mutual funds, shares with the tax authorities.
- Double Taxation Avoidance Agreements (DTAA) – Countries Involved, Income Tax Provisions
- UPSC Mains General Studies Paper-III Strategy, Syllabus & Structure