Ms. Parikh said some customers had shown up with suitcases of cash, beseeching her staff to pretend that the purchases were made days earlier, which the staff refused to do. Some other luxury goods stores not only obliged customers but solicited them, sensing an opportunity, Ms. Parikh said. “Everyone has tricks up their sleeves, backdating bills,” she said.

Real estate has been particularly hard hit by the ban on black money, since sale documents filed with the government typically reflect only the portion of the sale price paid by check. As a result, the sellers have no way of explaining to the tax authorities how they received the cash, which can account for as much as 60 percent of the deal.

People who had just sold property were particularly out of luck, since they have not had a chance to spend or invest the cash they received. One man who had just received 3.5 million rupees, or about $51,000, in a real estate sale said he was hiring 14 low-income people to deposit the 250,000 rupees in old notes that they are allowed to put into their accounts without raising questions. Such tactics, called bundling, are illegal in the United States.

Whether these schemes are successful will depend on the scrutiny of bank officials and the tax authorities. The Modi administration has said it will exercise extreme vigilance to prevent them, but the Indian government’s record in the area of corruption is not strong. Nevertheless, the pledge to crack down has ignited such fear of future income tax investigations that some people have been dumping cash. Several garbage pickers in Mumbai have found pillow cases and sacks filled with cash in recent days, said Saumya Roy, the chief executive of the nonprofit Vandana Foundation, which makes loans to the garbage pickers, among other low-income residents in Mumbai and elsewhere.

In a country where government oversight is weak, it has been easy to transact business in cash and to avoid taxes. Paying cash was also a way of avoiding the scrutiny of tax authorities who might question where a family, particularly that of a politician or wealthy business owner, had amassed the resources to spend enormous amounts of money on real estate or a wedding. “India is so crazy and complicated,” Ms. Devidayal said. “The option of not having black money is very much there, but because it’s so habitual and easy, and you can just say, ‘I had to do it,’ many people did.”

Cash had become so ingrained in the real estate industry that it was difficult to make a deal without paying some portion under the table. When Ramanan Laxminarayan, a Princeton University senior research scholar, tried to buy an apartment in the New Delhi area, he was told that he would have to provide 60 percent of the purchase price, about $420,000, in cash to close the deal. Unable to raise such sums, he gave up trying to buy. “I said, ‘Is it legal?’ They said, ‘Of course not,’” Mr. Laxminarayan said.

