They’re just cautious. If they mess it up, it could be months before your hair looks right again. I also ease into things when I think the person making the request doesn’t understand what they’re asking. Mind you, my clients are hiring me for graphic design, where my time is billable by the hour, and anything I do can be undone. I can afford to do exactly what they ask. (You know, unless they think I’m fucking with them to pad my time and use another GD. Then I guess I can’t afford it.)
Have them keep revising the trim until you’re happy, then ask them to take pictures on your phone of the views they as a hairstylist need to see. Show the pictures next time, so they know you know what you’re asking for.