That damage is spread across what seems to be a 3 or 4 inch area. If that happened in transit, then either the bass was moving around freely inside of the box it was packed in, the box itself would show substantially more damage, or both.
Otherwise you could see an ugly gash in one area, but not this.
Also, to my eyes some of those dents look newer than others.
I think this seller either did not realize the bass was damaged in this location (unlikely) or chose not to disclose it, hoping to complete a sale with a buyer who either would not care about the damage or who would accept a token refund, like $50. A bit crummy but that is how people are.
I see more than a $50 issue here though. If you like the bass, negotiate to $200.