+1 for not hearing a bad word.
I think its beyond tough, you'd have to deal with all sorts of individuals to which two people could receive the same level of service and one rate it 5 stars and the other 3 - completely out of business control. No doubt in the past you will have served customers with a 15yr old 350z, who has paid for a remap and wanted 315bhp from having just an exhaust and intake. Guess what type of review this person might give.
Is it possibly for a company to drop the ball - yes.
Would this happen, do I believe a Abbey would look to put the matter right - yes also.
Of late the majority of people will be under stress, the likes that aren't normally experienced. Repeated occasions of stress/worry/anxiety, by design puts us into fight or flight mode lending thoughts to materialise from the back of the brain rather than the rational frontal section. Thus things will be said and done that ordinarily wouldn't, given their right mind. There are only two reasons why a person would act adversely to another, jealously or stress aka not thinking correctly due to a lack of intelligence for that given moment - nothing else.