You could just look up how cheap you can order shit like that on Alibaba and know for a fact that it's true but whatever.

Dropshippers do that amount or round it, how do you think there are so many of them? Obviously this excludes advertising

if you're early to a rare niche, you can make way more than 600%. but depending on the niche, amazon might decide to compete with you (since they have all your sales data), or your supplier sells to anyone so eventually you get 10 competitors, then eventually your margin drops, but you know it is possible to keep your niche a secret for years.

These days you're guaranteed to be late to almost all possible niches, so if you don't have some inside knowledge/connection, you're probably gonna not going to find any niches that aren't already over-saturated.

The problem is even worse because grifters have moved on to selling "classes" on how to join this money making opportunity (aka scam), conveniently leaving out a.) how late you are to the game and b.) how the market has already pulled up several ladders.

They're selling lazy wannabe entrepreneurs a get rich quick fantasy that no longer exists and probably wasn't that great in the first place.