I agree with the sentiment that it should be nearly impossible to be "perfect". I used to be a waiter and in the busy days we used to do the best we could, but also in my experience we couldn't give the best performance cause our setup in taking orders. If you want player to have a more complex experience to earn a "perfect", it would be interesting to have further customisation on how the cafe works, like an advance interface with nodes (almost like coding in Unreal).