When I saw the title, I thought you were asking if I ever give 100% effort in anything I do and I thought that was a very interesting question.
But as to the question you have asked, yes, I do sometimes give full marks to student work. Of course, I do it most often on objective tests where I can't deny a student has gotten everything right. But there are times I do it even on more subjective things. My reasoning is that a person can do everything that I would expect from a high school student. It doesn't mean it's perfect work, just that it's all of what I could have expected.