Phone Cases Print On Demand Possible Issues?

Hey guys, I’m thinking into getting to the print on demand business, by setting up a Shopify store with a print on demand app such as Printful. My main concern is the quality of the cases. I’ve seen a couple of phone cases ads doing well, but I noticed a lot of customers complaining that the cases are of cheap plastic and that the illustration quality is not as advertised. Today, I saw a retargeting ad and literally all the comments were complaining it was a scam, cheap quality, that they wanted to return the case. (I guess this ad was targeted to people who visited the site because I did). Someone even created a Facebook page to expose this kind of “Scam”.
So could anybody give me some ideas about this print on demand phone case market, if you guys get a lot of returns, if it’s worth etc? Also, do you guys recommend any company that offers high quality prints and cases?