I'm not going to tell my teacher about a question she missed while grading my test
Why wouldn't you tell your teacher what she missed?
The grading guidelines were unclear and I'm not sure if the marking was fair so to avoid trouble I'd rather keep quiet. I want a good grade too.
That is wrong to take advantage of your teacher like that. The grading guidelines may be sketchy, but don't lie about it. She'll find out anyway.
I know that lying is wrong but I am not sure that telling the truth will solve anything.
I just think it's your duty to inform someone when they've made a mistake, even if that mistake is to your benefit.