Every dog is different and their personalities can vary as much as peoples can.
I have had pups as young as 4 months sail through the whole grooming process without a whimper, but equally I've had pups that are very frightened of the whole process.
The grooming salon can be a scary place for a nervous dog. There's lots of smells, sounds, sensations and it can be very overwhelming. Dogs that are overwhelmed can get too stressed and can start to snap and bite. I don't want them to get that fearful, as I'm sure you don't.