This achievement will unlock along the path to earning the "Hyper Shopper" achievement. This one only requires that you purchase the four assistants (sauna person, masseuse, bath person, and cashier) and upgrade them each one time (all that the game allows). The assistants will not all become available until later in the game.
NOTE: Do not purchase the cashier assistant until you earn Perfect Score on all 25 levels. Doing so will make the game much more frustrating and difficult to earn Perfect Scores, as the cashier assistant will automatically cash out customers, even if they do not have 5 stars.