It's all depends we choosing a project.. If you want a good quality bounty, just follow the most trusted bounty manager, find project who have a strict rules for participant (strict rules have possibility to avoid who cheat on bounty).
I agree with you. We must really filter the bounties that we have to join in order not to waste our time and effort in helping the project to be successful by doing our tasks. About the Bounty Manager, that's a good factor but we should also do the work on researching about the bounty to join. If a Bounty fails, it is not the Bounty Manager's fault I think. Strict rules are okay for me if it will scammers to come in.