South American clubs have to sell to survive, as Boca Juniors president Mauricio Macri is well aware.
"The economic differences between here and Europe are very big," he says.
"There, the players can earn 10 times more. And if you try to pay a star player the same as he would get in Europe you break the club's finances and destroy the harmony of the dressing-room."
There is no way of stopping the best players from crossing the Atlantic. So from the viewpoint of the selling club, two things should be important - that the star player fetches a good fee, and that he stays long enough to win titles and help attract a new generation of supporters.
"You should hope to have such a player in your first team for three years," says Macri. "One for him to adapt, and two to enjoy what he does."
Macri certainly got Boca a good fee when they sold Fernando Gago to Real Madrid. The Buenos Aires club will receive more than 20 million euros (around £14m) for the 20-year-old.
But Boca were not able to get that final third year out of their highly-talented central midfielder.
Gago made his debut towards the end of 2004, and won a regular place in the starting line-up during the course of the following year.
He was then a key part of the side that won the next two Argentine championships (two are played per year) and narrowly missed out on a third earlier this month.
After a year's absence, Boca are back in the Copa Libertadores, South America's Champions League. They wanted Gago to stay for it, and then move on to Europe in the middle of the year.
But Real Madrid wanted him now, and crucially the player was desperate to go. So desperate that in the negotiating process he waived his right to the share of the transfer fee - a small matter of 2.7 million euros - to make sure the deal went through.
Gago is a grizzled veteran compared to Real Madrid's other two South American signings. Striker Gonzalo Higuain was not even in River Plate's list of 25 when they named their 2006 Libertadores squad back in February.
He was drafted in at the end of April for the knockout stages, came off the bench to score two vital goals against Corinthians and hasn't stopped scoring since.
Now he joins perhaps the world's most glamorous club with a total of around 40 first-team games behind him.
Eighteen-year-old Brazilian left-back Marcelo has had an even more dramatic 2006. At the start of the year he was not even on the Fluminense subs bench.
But when he got into the team he made such an impact that he was almost immediately called up to the national squad. He made his debut in September against Wales at White Hart Lane and capped the occasion by opening the scoring with a wonderful solo goal.
Then he and his Fluminense team-mates suffered a collective loss of form - one time leaders of the Brazilian Championship, they finished the campaign fighting off relegation.
And now he is being groomed to replace Roberto Carlos.
Higuain and Marcelo barely got into the second six months of Macri's three years before answering the call from Europe.
Their clubs have made money from the sales, but missed out on the benefits they might have reaped by keeping such emerging talents a year or two longer.
As for the players, time will tell if they have jumped too soon.