MIMF

I need help, if I stain a fretboard with a water based stain (designed for wood, obviously) will it mind that it will eventually fade away with time if I leave it unfinished? (environment moisture that might dissolve the stain?) or will I need to give it a coat of sealer in order for the stain to work for a long period of time?

I have a walnut stained fretboard with the frets already in and I would like to know if it's crazy to leave it unfinished, the natural wood of the fretboard is not "that" good and with the walnut stain looks amazing (rivals a good rosewood fingerboard, half the price and plenty supply of it), and this same for a fretless instrument like a violin (for example), would the stain fade away with the string use?

the guitar I'm planning it on selling it, if it where for me I would had no problem in re-staining it once a year, but might look like a fraud for the one who buys me this guitar.

would an oil finish be compatible with the stain?, the wood I'm using is Cumaru.

know that I think of, I should test on scrap and tell here the results I get xd, I would still love to hear the opinions and experience some people here might have.

Water based stain or dye is not suitable for a fingerboard. It can look good for a while but the new owner will get color on his or her fingers as it is played and fingers perspire.

If you polish a scrap of your fretboard wood will it have a nice appearance? Maybe you don't need the added color.