There's some percentage of people that always want to pay the lowest price and if the product turns out to be fake they return it. Say you order 100 things over a month and 5% turn out to be fake the only cost is time (Amazon pays for shipping if the product is fake I believe). That's compared to paying 10% more on every product plus the time it takes to go to the store.
Honestly if I can’t trust that a company is delivering a real product or not I’m OUT. That’s a violation of trust. And it’s happened to me multiple times on Amazon—nowhere else.