The thing is, they formulate box color for one type of hair, and that's extremely coarse and resistant white hair that needs the most coverage. With that being said, they use stronger chemicals and developers than needed to cover your hair. Also, they don't teach you how to properly choose pigment, Trust a professional who formulates for your exact hair type and color.
The hairstylist is sometimes right. This one lady I went to literally tried to dry brush my hair which is curly and had gel/hair spray in it (i live in a humid client). It hurt really bad and I begged her to wash it, but she just kept going. I refused to pay and talked to her manager.