1) I am not modelling things to be sold as a standalone product (cell-phone case, etc). I am using my printer to make things that are a) parts of bigger items to be sold, b) are important inner parts that aren't even seen, but they aren't necessarily the object sold themselves... At the end of the day, people are willing to and are paying for my items, whether they know it or not.
2) since they are parts in a system, as opposed to phone cases or chess pieces, my concerns are very different than any of these, but I have patented the systems/objects I make, so theft isn't so much my concern... The systems are much more than printed objects, I actually posted one to Thingiverse, offering to send out some free parts (arduino, LED's, etc) to any one person who was willing to actually make one. No takers. It's alot of work to make the stuff I am working on.
3) how much is a phone case in a store? how different or custom is it than what can be readily found? I've seen some really cool multi-colored printed phone cases that are truly unique... If someone came in with their design, and i printed it for them, then it's isn't selling them a case, it's providing them a service...
4) probably not, I'm already not buying stuff because I can make them for myself.
side note: My phone streaks around with no case... and it's proud to do so. ;-)