When the National Association of Realtors signed a landmark $418 million settlement in March, economists and academics predicted that the deal — which included an agreement to upend key practices concerning how real estate agents are paid — would create the most significant shift to the industry in a century.

The real estate industry is resisting the changes that go into effect on Aug. 17.

“A lot of agents have been sort of lulled into the idea that Aug. 17 isn’t really going to happen,” said Laura Ellis, a broker in Chicago who serves as chief strategy officer and president of residential sales at the brokerage Baird and Warner.

The settlement makes it clear that agents can no longer discuss splitting compensation on the online databases, called the multiple listing service or the M.L.S., that they use to list homes. And Michael Ketchmark, the lead lawyer in the successful lawsuit against N.A.R., cautioned that agents who seek to move the commission conversation to other venues would be opening themselves to potential legal fights.

“Anyone who thinks they can continue to fix commissions on new websites or side deals is foolish and wrong,” he said. “We will take legal action to enforce the settlement agreement. It’s time to let the free market finally work.”

The Department of Justice, which reopened a yearslong investigation into the trade group after the settlement was signed, continues to investigate N.A.R.’s antitrust activity as well.