I joined a lots of bounty campaigns here on btt recently but I have encountered bounty campaigns never paid the bounty hunters at the end of the campaign period. Not to mention these projects, some of them are now scam, but some of them are now very successful after the campaign, and they forgot to pay their advertisers at the end of the bounty period. As a bounty hunter like me , its very important. Its really pain when you are advertising an ICO for month/months but in the end you got nothing. As of now, I only joined a bounty campaign which handled by bounty manager with good record here.
Unfortunately recently, many projects are cheating and offending bounty hunters. I believe that you need carefully study the project's perspective and see how the developers will interact with users. Perhaps in the future the guarantor will be used to ensure that bounty hunters are guaranteed to receive a reward for the work done.