If one considers the immense range of subjects that is covered in each episode it is unlikely that any but a full time quizzer is likely to score say 90%+ correct answers. I have a lot of knowledge - if you only ask me the right questions ;)
Mark often refers to the Dunning-Kruger effect where people think they know more than they actually do. Some contestants suffer from that but others suffer from nerves and seem to freeze under the lights.
Because they are very good when they watch at home. A poor performance on the show can be down to bad luck as regards the questions or panic - or a combination of both
Tenable, name the 10 countries with exactly 7 letters that are between G and M (or something like that), sadly Georgia, a university student, couldn't think of one! Even her team looked embarrassed for her.
Having been on The Chase (14th Dec) I can say its a tough route before you get there. A few phone calls and interviews plus a dummy show with the producers.
So, a dummy is not going to get through to the recording....unless..that is what the producers want...