To provide you with specific answers, we are going to need some more information about the bass you are selling/looking at buying.
However...
Old basses generally have a bass bar crack or two. It happens, it is wood, and it cracks, especially near the bass bar/saddle/lower ff hole. If the crack has been repaired well, the value shouldn't automatically be reduced. The value of old basses is going up and up all the time, and much of them are riddled with cracks. It all depends what you are looking at, and the condition of the rest of the instrument.