Informa is a great company to work for, but they do require a lot of detail in their shop reports. I don't know if I personally would have been comforable doing their shops when I first started out mystery shopping.
If you are already scheduled for it, I would make sure you read everything very carefully, and maybe call your scheduler to go over the details with him/her.
I have never had any issues with contacting or talking to them, and my shops have always gone through without any issues. They can just be long and time consuming.