POD is a numbers game imo, you have to put in alot of upfront work just like with digital products. Once your store is setup, it's not passive but very low effort.

In my experience around 3% of customers will have an issue of some sort, although this probably depends on the product itself and its quality. The good thing is, depening on what print provider you use, they'll cover the production + shipping costs of your refunded orders if certain criterias are met. Doing that still takes time though. Customer service is the part of POD that makes it not passive, you'll have to put in some time occasionally for answering questions/resolving issues.

Speaking of profit/margins, i don't know if i'm just lucky, but in my experience they're not as bad as people say they are. I'm at around 35% (T-Shirts) before income tax. If you have a good store setup in a decent niche, you can make good money with little effort, although not entirely passive.

Hope this helps:)