I completely agree with
Successcrewleader . He has nicely explained idea of dropshipping. It is a type of business model that allows entrepreneurs / retailers to start a business and sell products to their customers without ever actually stocking the items themselves. They can place an order from manufacturer or a wholesaler to ship goods directly to customers.
To add to the above I wrote, if you now also add in product arbitrage, which is essentially is taking a product listing, and make a new list on a different platform, offer it with a markup plus a reasonable amount for shipping and any potential tax, then when an order comes in, you very simply just order it from where it was originally listed using the customers address information for delivery. Your profit would be difference between what your customer paid you and what the actual total expense. This is repeatable and scalable, and works with almost with any sort of niche, and don't worry about market saturation, there is more than enough to go about.
In steps:
1. Identify a profitable listing.
2. Create your own improved listing on a different platform.
3. Market the listing - advertise it.
4. When an order comes in - process the order (order it and mark it fulfilled).
5. Rinse and Repeat.
To give an example of the above.
1. You identify a dental care product which seems to be in demand.
2. You create an improved listing based on the original listing, using the same images or better ones of the same product. You list it on for instance Ebay or your own website.
3. You create an ad, then either use an Instagram influencer or Facebook for advertising.
4. An order comes in, you review it, proceed to order it using the customers delivery details, then mark it as fulfilled.
5. You keep doing this as you see fit.
If there is an interest for it, I can create a much more thorough guide, if there are enough people interested in it.
Dropshipping & Private labeling, both are topics I know a lot about, and very easily can help people with.