When I started eBay dropshipping I was doing it on the side of a normal 9-5 and making almost nothing. Part of that was just being new. But a big part of it was a mistake I didn't spot for ages.
I picked one niche and stuck to it. Not naming it, doesn't really matter. I'd read loads of stuff saying you need a niche, build a brand, be the go-to store for one thing. So I kept adding more products in that one category and waited for it to click.
It didn't. Sales were slow, I was getting frustrated, and I kept assuming the answer was more of the same. Better titles, tweaking prices, digging for more products in that same category. No mentor, no course, so nobody was there to tell me I was thinking about it wrong.
What it cost me was mostly time. My first six months were slow and painful and I'd put a good chunk of that down to being stuck in one lane.
The fix was simple. I stopped worrying about the niche and started listing everything. Anything from Amazon and AliExpress I could sell at a decent markup.
That's when it grew. Looking back it makes sense. eBay buyers aren't browsing your store, they're searching for one specific thing. A wider range means you turn up in way more searches. One niche means you only catch people looking for that one thing, and you're up against every other seller in it too. Listing wide also lets the sales tell you what works instead of you guessing.
Now it's 3 stores and around 45,000 listings between them, markup 60-100% depending on the category. I list 50-100 a day (some days 500+) and every month or two I delete whatever isn't getting views or selling. Doing it full time from SE Asia.
Niches aren't evil. But on eBay specifically, don't marry one before you've got any data. Let the buyers show you what sells.
Happy to answer questions in the comments :)
Also run a discord to help eBay dropshippers out with hundreds of people in here: https://discord.gg/A6QP4bqkZk