Your models are all very specific: spaceships and jewellery. Spaceships probably need more detail, like windows, engines, landing gear. Now they look like they are made from one piece. Presentations are good, I advice to also add clay renders and wire-frame views to show customer the topology. Do some research, search for similar models for sale, check your competition. Ask yourself: is my product better, how can I make it better. Also research the market before making something, sometimes you can find so many competing good quality models that making another one makes no sense. Unless you can make one that is better.
I can not say much about 3D printing and jewellery, I guess people either like it or not.