yeah, in market there are lot of fake cosmetic. You may found Mac, Bobbi Brown selling at night market with a very super low price. Even some selling the limited edition >.<"
For anna sui, benefit, loccitane also have fake product, but most of it can find in country like china.
Normally if want to check the authentication, first is check the packaging. Normally fake product packaging will different from original, eg like the product code, import code, especially the wording. Then the bottle design also might have different. Another one is the smell~