Yes, I believe that if someone acts or thinks that they are not smart they will not apply themselves to at least try. If they do apply themselves though they could be considered smart. More work generally means that you will get better grades, so it does depend on a person's IQ in my opinion.
Yes, because your personality will reflect how smart you are based on how you act. If you a high IQ then your personality will include having a large vocabulary when speaking to others. Whereas, if you have a low IQ people probably would not think of you as someone to ask for help.
I tend to disagree; sometimes, lazy people are smart, however, they choose the easy way out instead using their full potential. They can have high IQs and only use their ability when they it is really necessary. For example, students can stay out of school and come back to out score students that were there everyday.