It is really hard to detect scammed bounty campaign. After completing all the requirements to be able to get accepted in a bounty campaign, spending much time to participate in forums and not to mention carrying their banners, completing all the tasks and reports then all of a sudden you will just find out that you have been scammed already. luckily I am not the only one but to think all participants did the same efforts as well as you did. But it is really happening, lesson learned and could be just charge it to experience and move on. If we could only find out at early stage if we were in to scam or a legit bounty campaign. Who would really know anyway?
You're right, in fact, none of us can know for sure if the chosen campaign will be fraudulent. The rights of the bounty hunters, as well as the rights of those who take part of the ICO are not protected. We all just have to hope for the best.
Of course, we can partially protect ourselves by analyzing the project, finding out more information about the development team and the funds that are investing in this project. But still it can not protect us for sure.