Let me remind you of some basics before we start to grind this achievement.

In the first building you can't have ANY barbers.

In the second building you can hire only ONE barber.

You want to get to the third building as soon as possible because it unlocks the two remaining slots for barbers so you can hire THREE barbers at once.

After getting to the third building you should buy every piece of furniture first and then hire 3 barbers. I won't tell you how to do it because there is an excellent guide on how to do this already. Just follow the steps in the guide below:

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=809215916
What is hard in this achievement? In each career you only have THREE spots for barbers so it will take around 333 games to do it. But not if you do it my way.

After you followed the guide above just idle and get as much money as you can. You will need it anyway because there is also an achievement for getting 100,000,000$ across all careers.

When you see that the next rent is gonna end your career sell every furniture you have and fire all barbers. Then just click on the computer and hire 3 barbers and immediately fire them. You can get up to 100 barbers in one game so instead of 333 games it will take you around 10 or 20. Much faster, eh?