There are some strategies to prevent Amazon from destroying your business, but you have to be very careful.

I know people who make 3k+/month with a 3-5k+ investment. They don't really care that it doesn't work anymore for that specific product after 4-5 months. The ROI is crazy. But most people don't know how to do this properly and lose money. For these people it's basically gambling and I wouldn't recommend it. It's hard to pull it off consistently.

edit: OT - is it just my perception or is HN more interested in passive income sources lately? (also making passive money with SaaS like the projects on indiehackers.com)