Anyone who calls himself an exam prophet is either overselling or overestimating his own abilities.
I can think of a few broad categories of students who engage tuition teachers. These students want to improve their grades, but not all will find the tuition experience helpful.
Some students will only do tuition homework, and not think beyond the immediate question/issue/essay. These students will not perform well once the question is changed. Some students do so much homework that they can see a pattern to the questions in exam papers. They will get their desired grades, but may not understand the subject comprehensively. Some students can eventually make the mental connections to draw a good mind map. They can then sack the tuition teacher.
Students who do not go for tuition usually prefer learning on their own, but may also be smart, poor, or academically apathetic.