Reducing/covering your scent to the point that it doesnt spook the deer is the key.
If a deer is downwind of you he will smell you. To what extent depends on alot of things. I use cover scents alot and firmly believe in them. I have had deer directly downwind of me doing their best to get a good wiff of me but the reduced scent and cover scent hid me just enough to keep them from spooking. Cover scents do work but you have to have clean hunting clothes and a clean body to add to it.