If the manufacturer sends directly to Amazon, you will pay a bit extra to attach the Amazon labels or for any needed packaging. By packaging I mean things that you buy in bulk like USB cables. Somebody needs to put those in plastic bags or something.
Things that you can send in directly are those you find at second hand stores, garage sales, or retail clearance sales (retail arbitrage). The tough part, I understand from research, is finding items. You can easily spend hours searching locally for items to sell, so some sellers turn to overstock pallets or private labeling Chinese junk.
I didn't get fully into it because I sold my account. The ideas I found were things I already used locally. I checked the prices on things I bought and found a couple of items that I could buy endlessly and resell for a bit of profit as part of a diversified inventory. Most people don't give concrete examples because it crashes the market, but I'll give you one: quality markers (e.g. Faber Castell) that I buy at the local university cost $5 or $6 for a package. The same package sells on Amazon for $12+. It seems like small profit after fees, but if you have many such items selling every day, it can add up. They are small to ship, inexpensive to buy, and always in stock. If you can find the wholesaler, you'll do even better.
If you are overseas, you must consider the cost of shipping to Amazon. See if there is something locally that people want. If it is not already available on Amazon, you can buy UPC codes for it and list it yourself (or try GTIN exception). Use the Amazon seller app to scan items before you buy anything because some things are restricted, like certain brand names or movies. You will see the fees in the Amazon seller app, but not shipping. The fees are high, but they store the item, box it, and ship it. If the item does not sell after a few months (?) they charge more fees for storage or you must pay to return the item to you or pay to destroy the item.
