If you join a bounty or have interest to join a bounty, you should pay your attention on its past operations. I meant if the bounty has run for weeks or months, you should check whether it delayed its payments for participants or not.
For example:
If a bounty originally announces that it will run from Jan. to Apr. (of 2019, for example), but then when April passed, there is no payments, and they announce to expand bounty for another 3 months. It is a good signal of bad bounty, and participants will highly not get payments at the end of that bounty.