I would guess that half the time the student just wants someone to tell them the answer.  In effect, italki becomes a homework factory.  Instead of working through the exercises themselves, they just ask on italki, and someone gives them the answers.  It's like copying your homework from your friend, except that on italki your "friend" is really, really good at it and always gets the answers correct.

I remember once that I really pissed someone off because I asked the person what he thought the answers to his questions were.  He was upset, and expected me to just tell him the answers.  He did not want to have to think through the questions.

I usually go by the method of elimination. I see that B and D are obviously not correct, and then I concentrate on A and B. I will either guess or leave it blank. Why would I leave it blank? Well, sometimes, I feel embarrassed to say something extremely absurd and obviously false in front of my classmates or to make the teacher feel disappointed in case we've gone over the same thing many times in class. But if I feel comfortable in the classroom environment, I may as well guess. Many times, I find myself itching to choose B over A but I just don't want to take the risk. And then, boom, it's B, just as I had suspected. I am left regretting my lack of belief in my abilities. I guess I should just trust my intuition and ignore the pressure of the environment. So, I think you're right about the 'doubt' thing.