The smell makes playing it an unpleasant experience to even consider.
I have bought a few basses that smell like rotting mildew (especially the cases they come in), and what I've come to realize is the people selling them are genuinely oblivious to these odors. They are probably just so used to these smells that they don't think anything of it. I once bought a project bass that smelled like a bowling alley dunked in cigarette juice. It smelled so bad that I ended refinishing it because that smell was soaked into the finish