@devincamary I often groom right in front of the owner, doing house calls some people go about their day, other people like to watch like it's a performance art show and others will actively help (especially if the reason I'm making the house call is grooming aggression then they're often on treat dispensing duty)
The one thing I cannot stand is when the dog reacts to something I do (picking up their paw, singling out a nail shaving a sensitive area etc) and the owner starts telling the dog no or bad dog and doubly so if the dog is giving a warning bite with a soft mouth-- I know that usually they're just embarrassed by their dog's behavior, But then I have to start explaining how typically the dog is not lying. Either picking up their paw hurts because they're oversensitized from the nails growing out too long, or they have an issue with their knee etc and it's actually the sign of a good dog that they are not using any pressure or are warning with a growl that they are uncomfortable. I start with a half truth where I tell them that when they yell at their dog for reacting the dog just thinks that they're yelling at me, that usually gets them to stop, then I have to say something to the effect of "I don't care if he bites me" ( I do) " I want you to tell him he's a good boy because he is letting us know what he can't handle"
Usually it's not serious the dog's not actually biting just giving big reactions until the dog starts realizing that I will respect very small reactions, Then they calm down enough to take treats and have a happy appointment where they are communicating calmly.
I totally forgot it's even worse when people yell at their dog for the small reactions like jerking their paw away.