I remember reading an article a long time ago...

wait here it is:

https://www.cringely.com/2009/03/14/parrot-secrets/

This guy had found a niche for an online business.

I can't help but wonder how many competing cookie-cutter copies of the businesses were started the day that article was published.

Actually sometimes a dropshipper will be willing to say what sold really well last year (if they're seeing poor sales on that item during the current year).

It's not hard to figure that out, make bunch of fake Facebook accounts in different age groups and disable ad blocker, you'll get bombarded from ads on store.

Then go to that advertisers profile and checkout their all running ads on their page, you can easily Google how.

My sister does this and she was a hairdresser so she mostly operates in the beauty product sector but also has had a lot of luck with things from IKEA this year.

The generic product area like clothing or whatever is probably ok. Got to protect the secret sauce though.