There are so many bounty campaign that moderate by newbie with 2/3 activities, is that kind of bounty are safe and believable?
The fact alone that the bounty is managed by a new member of the forum is no indication that the bounty is a scam. Some projects just decide to manage their bounty themself and therefore create an account here to do that.
Of course the risk of a scam bounty is higher with a new and unknown bounty manager compared to those campaigns that are managed by the well known and appreciated bounty managers here in this forum.