I really think most people are smart enough to decide for themselves. If the dissatisfied customer tells people that aren't already using the wash, they might never have used it anyway, so there's no harm. It's not like Teebox went after her car with a baseball bat, so if she tells people that are already using his wash what happened and they have no good reason of their own to go somewhere else, what can she tell people that will change their mind? It's not like a dryer falls on a car every day.
If someone I trust tells me to try someplace because it's great, I'll probably try it. If someone tells me that a place I go to and like did something bad that will probably never happen again to anyone ever, I'll keep going back.