I started my polymer clay life as a miniaturist over 30 years ago and now sculpt non-miniature faces and hands and other fine designs for our molds. To perfect the surface and remove any blemishes I've created a series of sanders using dental bits.
The gold color bits are super fine and the silver color bits are fine.
Also good are red and white stones. Red stones are the roughest, white the smoothest. Start with the more coarse stones and move to white.
I put these bits into handles made from old paint brush handles, dowel rods, acrylic rods, what ever I have around the studio that will work.
These tiny sanding tools allow me to smooth tiny eyelids, lips, etc. for broader areas I use tiny strips of very fine sandpaper, folded in half with the grit side out, to smooth the surface.
Since I do not make dolls to sell, these may or may not work on the face and hands of a doll. Something to think about or experiment with.
I've attached a link to an image of some tools that I quickly scanned so you can see how many types of handles I use. The metal ones are very heavy to me and I prefer the lighter, wooden ones. https://www.flickr.com/photos/pennijo/15946362360/