When it's the transfer period. Go to "Transfer Central" and select "Transfer Market". Press R2 and go down to the bottom of the selection menu and change it to "Free Agents". Then select the best free agent you can. Put his wages full and his percentage bonus to 15%. You should sign them unless you're a lower league team. You might have to renegotiate and increase his wages again. Once you've signed the player put him up for sale. You'll 100% of the time make a profit, unless you sign someone on the last day of the transfer period as you might not sell them in time. Once they're sold you'd have payed them only for 1 or 2 games and make a huge profit.

I once signed Wayne Rooney as Wrexham, I played him 1 game and lost £150,000 but then sold him for £40,000,000. Total profit £39,850,000.
I got promoted two seasons in succession because of the money.

It works on all consoles.

Liverpool FC are the best.