Based on my experience participating in the bounty so far, i just consider the basic factor of bounty based on:
1. Ranking of the Website (at least below 300 thousand)
2. Number of telegram members and how active the group is
3. Their team, whether credible or not, (can be seen whether they have a linkedin account, and have connections)
4. The number of their ICO targets, the more the better
5. Bounty manager, choose the green trust or neutral trust.
Or for complete you can see here: https://bitcointalk.org/index.php?topic=2941946.msg30222695#msg30222695