Can you make money reselling on Marketplace?

Can you really make money by reselling on Marketplace? I've heard stories of people flipping items for a profit, but is it a viable strategy? What kind of research should I do before diving in? How do I know what items are in demand and have the potential for a good markup? Are there any risks or pitfalls I should be aware of? Are there any success stories you can share of people who have made a significant income through reselling on Marketplace? I'm interested in learning more about this potential side hustle.