Let's do the math ..

All three clubs have an average net spends of 20-30m a season for the past 5 seasons.

Yet teams coming up sometimes net spend north of 150m

Compared to their PL income, 20-30m net a season to keep up suggests they have expertise at player trading.
But we already know this.

They do well because they know exactly what a player is worth.
Once an offer vastly exceeds that they sell.
Just look at the list of players each club has sold over the past 5 years.
They have been able to build their squads by selling for top money.

Posted By: usacanary, Jun 28, 17:21:54