They need 'secret shoppers'.
I can assure you Pax, they do have them. Problem is the bar that BA have set themselves is now far lower than it used to be. So inspector says:"On my C-Europe class flight, toilets were less than clean, food was just about acceptable. Service was at minimal level required - but nothing special and flight was less than 20 minutes late" BA shrugs and say's "OK, good enough".
15 years ago, that would be a resounding "Fail". Now, it's "Satisfactory"
The report above fairly accurately mirrors my experience this last weekend.
As I sat in the 737, my mind went back to CE flights taken in the mid '90's - probably on the same aircraft, in the same seats. World of difference.