After you reach lvl 25, you go to the hair salon next to the store and get a job. It requires hair dressing skill of 25 to start. Once you start working there, your skill will raise every day you work until you get to 75. At that point you can either go to work at the nice hair salon, or go ahead and lease the empty salon.No, since, even you have the money, it remains impossible to increase your hair dressing level beyond 25 (The school is closed for you)
Exactly what I said is that if at any point you lease that empty shop, you skill will not increase anymore (except to 25 from the college) and you will not be able to work in either of the 2 shops for the rest of the game, thus skip an entire quest line.
This is a known bug that has been mentioned several times over the last few pages and it is being looked into and hopefully fixed on the next release.
So the answer is simple. If you want to work in a salon, then never lease that empty shop, train to 25, then get a job at the shop that requires 25 until you get to 75, then you can choose the fancy salon or go lease that empty one.