How can one with black hair tell if he or she has really bad dandruff or lice?

Location,observation: Young lice take ~10 days to mature & start laying eggs & do so at the hair line.Most infestations will be noted when the egg casings become evident. A tiny oval egg tightly attached to the side of a hair, with many others at the same distance from the scalp. 10d+the length of hair grown out ~ duration of bugs(u may never see them).Dandruff will be loose & flaky, in crusty patches on the scalp.

No problem: Dandruff will leave visible flakes on your hair and sometimes your shoulders. The color of your hair won't stop you from seeing them. If you've got enough lice, you'll sometimes see the insects moving around and sometimes maybe feel them crawling. You confirm by looking closely through the hair; if you have lice, you'll have nits(eggs) stuck to the hairs about 1/2 inch above the scalp.

Also....: Sometimes people who see something in their hair have trouble deciding if it's dandruff or lice. The way to tell is simple; if it's stuck to your hair, it's a nit (egg). If it falls off or you lose sight of it when you touch it lightly, it's dandruff.