I grew up in a tier-2 city in India, and the amount of black money rich people hoard around here is of ginormous proportions. Easily > 50% of the income for most rich folks.
Cash, money-laundering, sketchy real estate transactions (Benami- transactions under fake names), informal banking (hawala), the same as in most places in the world. Think early mafiosi in the US. The most significant legislative actions for curbing these are: Benami and Hawala legislations, computerization of land records in the late 90s and early 2000s, PAN numbers in the 90s and Aadhar in the last few years (a bit like SSN in the US), and the OP.