Rule Six is that you don't have to smell everything. Most perfumes have been practically studied by lots of people who have way better noses than you do. Smelling a lot of perfumes not only creates a huge olfactory blur, you're not even smelling perfumes as they really are. Perfumes will interact with a person's individual skin chemicals plus the top notes fade. Why not avoid most of the torture and find out the general type of fragrance you are shopping for.
If you know the brand perfume, skip this step. But if you don't, think of whether the person would want a floral scent (or something very modern right now, the fruity floral, which are for the trendy, the young, and those burdened by their own tragic hipness), a fresh scent (which is kind of like soap, very mild, and popular with people who are or imagine they are under 18), an Oriental or spicy scent (these are heavier and for mature women; I would even say they are old lady scents except I wear them. Let's just say they are much more complicated, denser perfumes that are very sophisticated. Here's a way to look at it.