The MLS has long provided a cushy home for some of the game's biggest names entering the final stages of their careers, from David Beckham to more recently Zlatan Ibrahimovic and Wayne Rooney.
But for Garber the most notable transaction was one going the other way with the Vancouver Whitecaps FC selling Canadian teenager Alphonso Davies to Bayern Munich for an MLS record transfer fee of $22 million ($A30.5 million).
Garber noted that MLS owners spend more than $100 million ($A138 million) annually on player development and the league is realising the benefits of that investment, with academy players this season producing more goals and more assists than any other year.
At the same time Garber believes the MLS must balance that spending.
"We need to become more of a selling league," Garber told a news conference ahead of the MLS Cup championship game in Atlanta on Saturday between Atlanta United and the Portland Timbers.
"We all need to get used to the fact that in the world of global soccer, players get sold.
"We have been buying for so long and as we’ve gone through the analysis, it’s hard to justify that investment and the investment that we have to make in player development.
"We’ve got to have something that turns this model around, or else it’s going to be unsustainable."
Garber held up Saturday's MLS Cup final as more evidence of the league's growth.
In just their second season Atlanta have established themselves as the model franchise, smashing records on and off the pitch.
This season, United became the first MLS team to draw more than 1 million fans and averaged a league record of more than 53,000 spectators a game, eight times drawing more than 70,000.
An MLS Cup record crowd of more than 73,000 is expected on Saturday, making it, according to Garber, the highest attended game in all of global football over the weekend.
Those kinds of numbers have left cities queuing up to secure a franchise.
Cincinnati will begin playing next season as the league's 24th franchise with Nashville, Miami and Austin to follow.
Garber said the league would award a 28th franchise within the next 12 months and hinted that expansion may not stop there.
"We will have to decide if we want to go forward beyond 28 teams," said Garber. "That is a discussion that is taking place, we will begin to introduce the subject at our board meeting later next week.
"I don't expect there will be an announcement coming out of that but there is no doubt in my mind that we can support more than 28 teams in Major League Soccer."