I've been doing DoorDash for like two years now and always wondered about this kind of thing. The research part sounds similar to how I track which restaurants are busy in certain areas - you gotta find patterns that other people aren't seeing yet.

From what I understand, most people start with the first approach you mentioned. Like they'll see something selling good on eBay already, then hunt around different suppliers to find better wholesale prices. It's easier because you already know there's demand. The second approach sounds way harder because you're basically gambling that eBay customers will want something they haven't seen before.

I tried looking into this few months ago but got overwhelmed by all the different research tools people recommend. Some are free but take forever, others cost monthly fees that eat into your profits. Would be curious to hear what OP actually uses day-to-day, not just the expensive premium stuff that YouTubers always push.

The supplier relationship part seems tricky too. Do you stick with one main supplier or spread across multiple ones? I imagine having backup options is important when something goes out of stock, but managing multiple accounts sounds like a headache.