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.

Varnishing

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:

Put player upside-down.
Put a couple of drops on the base and let gravity do the rest.
Let it sit overnight.

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.

Polishing

Choice of polishes:

Swiss-T polish which you can get at Subbuteo USA (see links page). That's a top polish but it is pricey.
Pledge (the furniture stuff). Never tried it but it is what old skoolers use.
Turtle Wax F21 (old name is 2001) Super Protectant for leather, vinyl, rubber and plastic surfaces (in the automotive aisle of WalMart or Target). It is actually very close to Swiss-T in terms of results and it is much cheaper.

Here is the procedure for proper polishing:

Put a few drops of polish on a polishing cloth.
Tap player's base onto where you just put the polish.
Tap player's base somewhere else on the cloth (to remove excess).
Polish the heck out of the thing by rubbing back and forth on the cloth (like playing Decathlon on C64).

Not that hard and mildly fun. Do it at the beginning of every game and you will be all set.