The SUBBUTEO technical page
There is no if's or but's! You have to polish the bottoms of your bases if you want to play the game. I don't claim to be an expert in polishing so you will have to take what I am saying with a ton of salt.
Disclaimer: you don't need to do this unless the base manufacturer explicitly says that it is needed.
But it does not hurt too much to try, right? You might want to try it on a single base before you go crazy about it and do a whole team. The idea is to put some varnish on the bases to make it flatter and smoother. The varnish I have been using is the one used for varnishing wood floors (water-based, looks milky white but dries transparent) but surely other types of varnish might do (I don't know). Now ... I don't mind putting some varnish on hasbro solids or subbuteo lightweights because they are so cheap. Not too sure I would try that on so-called pro bases that can cost a pretty penny.
Here is the procedure for varnishing:
You may want to devise an apparatus that keep players upside down or you could just remove the players if can be done easily. The important thing is to have the base as horizontal as possible once there is (liquid) varnish on it. Once the varnish is dry, the base is ready for polishing.
Choice of polishes:
Here is the procedure for proper polishing:
Not that hard and mildly fun. Do it at the beginning of every game and you will be all set.