Welcome to SaleHoo, Akrosoft!
This is one of the most common question we get on SaleHoo :)
While I'm sure no one will tell you outright of a niche product, I know many will give you tips. I'll do my best to help you on this one. A few things you might want to check are -
Your own shopping list: You might be surprised to find out that pretty much what is in your list is also on our people's shopping lists
Trends: Check out magazines, newspaper, tv, radio and internet - look for things/styles being repeated over and other again. If you find one, you've found a trend
Your friends/neighbors: When you happen to have a chat listen more slowly to what they say, you might pick up an idea or 2!
Your own hobbies/interests: It has been repeated so many times that you often succeed more easily when you are selling something you are passionate about. Starting out with a product that is related to your hobby would be good.
I know you are experienced with eCommerce but just haven't really sold that much so you might also want to consider selling things from around your home, things you no longer use. You might even uncover a niche while your at it, many have :) This is also the best and cheapest way for a new seller to get a feel of what it takes to sell online.
Here a guides with more tips -
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Also, links to related posts -
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Hope this helps you start off your business on the right foot! Cheers :)