At $25,000 per minute, advice from Donald Trump (search) doesn't come cheap.

That didn't stop thousands of fans from attending a Sunday lecture by the real estate mogul, who received $1.5 million for the hour-long speech.

Trump, star of NBC's "The Apprentice (search)," urged listeners to be aggressive and remain suspicious of advisers.

"When somebody challenges you, fight back," he said, according to published reports. "Be brutal, be tough, just go get them."

Aspiring dealmakers should work with others while maintaining a competitive edge, he told the crowd at the Learning Annex (search) event, which cost between $100 and $500 per ticket.

"Get the best people and don't trust them," he said. "Work with them, but they have to have respect for you."