I wouldn’t recommend printing and selling phone cases that have come straight out of a printer as there can be lumps and strings of plastic. However if your willing to correctly finish the phone case then it may work, but would be very time consuming. Despite this I’ve seen some very successful prints of phone cases.
If all of your cases are intended to be identical then I’d advise printing a few cases out of ABS or PLA until you get the right shape and fit. The reason for this is these materials can be easily sourced and are rigid.
Once you get the correct fit, sand and finish your model so that it’s smooth and make a mould. These can be cheap to make as an alternative to manufactured parts. It may take a little to get used to but at least you can produce for the demand.
Hope this helps. If you have any questions I’d be delighted to help you out.
