Unjustified written warning due to a mystery shopper! How can one proceed against it?

Question

Unjustified written warning due to a mystery shopper! How can one proceed against it?
It involves the following: My supervisor (franchise company) has received a cease and desist letter nearly a week ago. Reason: Due to a mystery shopper purchase she made, i did not get the magical 50 percent marks on my dealing with this lady. She gave me only 40 percent achieved! Blah blah, the 40 percent includes me being friendly, hygiene and responded to her in timely manner. Apparently i did not up sell by asking whether she likes anything sweet or sandwiches with her drink. This one sentence makes up 60 percent! It's a joke, isn't it? Friendliness etc. is less valued as this additional sales!
My question: Can I be given a written warning based on a mystery shopper? And if so how can i fight against it?
I was thinking of writing a letter to appeal against it, any help would be great.
Thanks for the replies!

Answer 1

If there are requirements to ask whats in the surveys, but mistakes are made or whatnot is asked, your colleague in the eyes of the customer just has failed. Whether then just a warning must be done remains. Before amn down however legally on it, she should talk and clarify its position.