Let me rant a little bit here...
I do not understand what people are thinking when they enter a store and do not take off their sunglasses. Unless you have a medical condition, I doubt that your eyes are sooo sensitive to the light inside the building. And no- recovery from an eye lift does not count.
Furthermore, do not proceed to point vaguely at what you want on the shelf or counter as though the person working can see you are looking at in the case. Hello- eye contact is important!