Cannot speak from experience cause I have never been at a dealership, as I'm aware of the toxic mentality within. This fact was confirmed by the old bloke I work for now, who said they are full of "bitches" (he never swears, so he really meant what he said!) who will go out of their way to sabotage you. Especially if you're good.
Being relatively green myself, I find working at this independent family owned shop fantastic.
I am NEVER pressured for time, and receive the right balance of guidance/ figure out shit by yourself. Even the couple of stupid fuckups I did (brake fluid on front quarter panel...oops. Or snapping a belt adjuster cause I did not loosen all nuts) my boss has never yelled at me or made me feel stupid. He could have. But he has been extremely kind, and just asks me if I have now understood the importance of guard covers :).
In turns he demands that I do not act like a smartass know it all, that I own up to my mistakes and do not make excuses such as time and pressure for my fuck ups.
He will never belittle me if I'm not sure and ask for advice when I get stuck. He will however get furious if I get cocky and break something cause I think I'm the best mechanic and don't need no advice (not me, seen it happen to my colleague).
My repairs often take twice as long as an experienced tech, BUT... the job is done right and I do not get comebacks. If I'm not sure of what I'm doing I ask. I have tremendous respect for this man and his business, and thank god he can see that this is my way of repaying him for the opportunity he gave me.
I work on all makes and models, most cars over 10 years old and within the 100-400'000 km range. I see a lot of interesting stuff, and many jobs are challenging due to the car being quite a shitbox. Every week I progress leaps and bounds, and my confidence builds up.
If i can give you an advice as a rookie, I found the main thing to make yourself appreciated is thoroughness in your inspections. During a service, I go over the car with a fine tooth comb. Hunt for work. When was the timing belt last done? How about the AC service? Transmission and diff fluids? How are the drum shoes and wheel cylinders? All that stuff that lazy mechanics don't bother to check cause you get filthy and use up time and energy.
He doesn't care if a service takes me 2 hours. He sees I respect his business and generate work, and I'm not here to wack in new oil and filter and collect my paycheck.