The majority of salons have a record card for each client listing colours used eg Wella koleston 77 blah blah. Even so I wouldn't let a trainee near my hair unless a senior stylist was present. So you did the right thing in leaving.
I think I have a similar colour to you. A dark blonde base with a few highlights. They only do the roots each month to hide the grey. The rest of the hair is left alone until I fancy a few more bleach highlights, probably 3 times a year.
It's the best way of making grey roots less visible. I also went into Boots and bought a root enhancer pencil thing .... Bit like eye shadow so you can temporarily touch up front roots in between salon visits. Haven't used it!!! Get my roots done every 3-4 weeks.
Hopefully it was just a blip with this salon. Not very professional but hey ho ..... Give them another chance ....
Heated Brush recommendation,please.