That is true. There are scam bounty campaigns and i also met several incidents like that. Further it is not easy to find a promising bounty campaign and i used to follow below mentioned procedure to identify the genuine bounty campaigns.
1) Use below mentioned websites to find the best bounty campaigns. These websites are publishing good ICO's and we can do that ICO's bounty campaigns.
www.icobench.com www.icotracker.com www.icodrops.com2) After selecting ICO's from the above sites normally i read all the whitepapers to get the clear idea.
3) Then i read their road map and team members as well
4) Follow all the social media channels and join the telegram groups to know the updates
5) Get the ideas from Cryptocurrency experts
6) Do only projects from good bounty managers.
Just follow these method to identify the genuine bounties. These days there is a good bounty called "Egretia" and it is the world’s first HTML5 blockchain engine and platform. Specially newbies also can do the Egretia signature campaign and can receive free tokens. Further they have several bounty campaigns like social media campaigns, reddit campaigns and blog/article campaign as well. For more information you can visit their bounty thread -
https://bitcointalksearch.org/topic/bountyegretia-the-worlds-first-html-5-blockchain-engine-and-platform-3316735 and if you like you also can do that bounty campaigns.