1) you are going to get a lot of people demanding refunds but not wanting to send the product back.
2) you are going to get a lot of people saying they never got their item.
3) people are horrible.
Also, pay attention to how eBay handles payouts and its fees.
If you have the right product eBay can be a great side hustle. Etsy is also a great option (if people know to look for you there.. otherwise it's easy to get lost in the noise).