Welcome to the site! If you search through the forum, you'll find tons of posts about ideas on what to sell. It may sound simple, but it's really difficult to decide on things to sell. One idea would be to start selling something you are interested in. Do you love fashion or movies? Perhaps you feel excited about the thought of new gadgets and technology. Chances are, there are other people who also share your interest - giving you an instant audience for your product. It's particularly good if you know where you want to sell. Your own store? eBay? Your own website? Flea markets? As Fudjj said, once you have decided where you are going to sell your items, you'd be in a better position to decide what type of products you should be marketing.
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All the best!