Unless you pay a lot more for the printer the finish isn't that good, not good enough to be on show (so to speak) and the plastic used doesn't respond too well to being sanded down.

 

I've had some recent experience of 3D printing for a project related to my work.

We had three prototype plastic parts 3D printed, the results were better than I thought, although at almost £1500 not cheap.

The pieces were all sanded, primed and painted