"We barred him, so he started to wait outside the academy picking out the cars of the parents, stopping them and tapping them up," said Ferguson.
The Scot, whose son Jason previously worked as an agent, weighed into the debate a day after his club captain Gary Neville said agents should be kicked out of the game.
The 65 year-old Ferguson did not entirely agree with Neville, but admitted the time has come for agents to be bound by more stringent guidelines in order to stem the flow of money going out of the game.
"In an ideal world, Gary is correct, but agents are here and I have no problem with players taking their advice," Ferguson said.
"But I'd like there to be an investigation into the payments or tariffs of agents. They are taking a lot of money out of football - so much so that clubs are in danger of not being able to buy players.
"That's a dangerous precedent because agents are starting to control the market because they are buying all the top players and that's happening at this moment.
"But if they were paid the same tariffs and same rates as lawyers and accountants, and had a responsible attitude towards the industry, then there is nothing wrong with that."
Manchester United, the only Premiership club that publishes details of payments to agents, shelled out a total of $3.5 million last year alone.
Earlier in the week, Neville said that he would like to see fellow players rely less on agents and take more advice from their union, the Professional Footballers Association (PFA).
"One guy can go in (to a deal) and expect to be giving hundreds of thousands or, in this day and age, even millions (to an agent) - and that money is going out of the game," Neville said.
"The clubs should keep that money - or, if they're earning it, the players.
"Players need good advice and good accountants - but they don't need people taking hundreds of thousands off them."