If the artist set license to non commercial then your basically allowed to 3D print it for your own personal use and noting ells, not allowed to redistribute the 3D data or the design in any way or form.
In 3D art you have two parts of a model that are copyright protected, you have the 3D mesh that is considered a unique creation constituting data in a specific form/configuration (usually a topology manually generated by someone). In most cases it also depicts some design that is also copyright protected, it can maybe depict something totally abstract, makes no difference, its a design nonetheless and its protected by copyright law. The model can also depict a design owned by someone ells, for example Mickey Mouse is a design proprietary to Disney, in this case the 3D model would be proprietary to the artist who made the model but the design would be proprietary to Disney.
Similarly you can 3D print a model and say your the owner of that 3D printed model, its your creation, however, that does not mean you own the design it depicts. If its a model downloaded somewhere then usually that design will not be your property and you will not have copyright on it unless that artist has grand you exclusive rights to own and do whatever you want with that design.
Basically, every individual needs to obtain a license if they want to use that design for 3D printing and only the real owner can distribute a legal copy of that.
If you have possible evidence on people selling copy’s illegally your always free to report it here so CGt staff can investigate and maybe contact the original authors, keep in mind some artist on this website also distribute licenses on other websites sometimes with different user name so its not always clear.
