Sanded fretboard.
 

I bought a bass with sanded maple fretboard. Should I do something with it? Not familiar with such a situation. Thanks.

So, I assume you mean it is an unfinished board. A little fretboard oil a couple of times a year wouldn't hurt. Keep it clean, unfinished maple can get dirty and start to look grimy.

^This.

If you have a can of clear laquer or poly, I'd clean the fretboard really well and then throw a coat over it.

Yes, it was finished before, but previous owner sanded it... So I suppose that finishing is not necessary?

Drastic changes in humidity will eventually cause problems with the neck if it's unfinished on one surface.

I suspected that... Any advice on laquer for maple fretboard?