There are twelve types of customers, each with varying levels of tipping and patience:

TYPE - CUSTOMER
Good tippers and impatient - Businesswoman, businessman, bride (pink dress with tiara)
Average tips and patient - Woman with brown skirt, man with grey pants, prom queen (little pink dress), male student
Average tips and impatient - Female student
Bad tips and impatient - Punk boy and Goth girl
Bad tips and very patient - Grandma and grandpa

Replay levels once you have newer equipment to gain more money.

-At the start of the game, save money to hire a hair washer and hair dryer. The coffee and a barista is kind of useful to have when you are having difficulty. Get the as many extras as possible as soon as ossible (for example, an extra hair washing chair, extra waxing station, etc.)

-Buy the candles as soon as you can since they are very helpful with impatient customers.