I'm disabled with similar disabilities as pert but not as severe. I have seen both types of disability questions and I answer them based on the assignment. In my mind, I am disabled for the purpose of a mystery shop if I can NOT perform the shop just as any one else. e.g. exit interviews typically require standing for hours. I can't do that. I am disabled when it comes to exit interviews. I am NOT disabled for the purpose of mystery shopping if I can perform the shop just as any normal bodied individual. e.g. Apartment shopping. Even with my cane, I can walk around an apartment and look at it as though I really needed an apartment. Apartment shops usually require that you come up with an objection. One of my objections is that it is on a floor that is a little difficult for me as a disabled person.
Bottom line is that I use my disability to help me as a shopper and it rarely stops me as a shopper.
When you learn, teach, when you get, give. Maya Angelou