Joining bounty is an investment. You are not paying your money but you pay your time, your work and other tasks to sit in front of computer for doing bounty. Put yourself on the side of investor who invest money, choose ICO and bounty campaign like you will invest your money in this, so you will take bounty campaign and ICO carefully. It is not 100% of all your investment or bounty campaign are good and legal but it will reduce your risk to minimum.
Yes, right answer chooses an investment ICO and bounty campaign are good. But I think choosing a good bounty is not easy, requiring a lot of experience as well as good analytical skills. In order to find a good ICO, you should have a team to analyze and ICO on social to be able to evaluate the most specific ICO. However, you can to select a bounty check website, team and bounty manager site is the best good bounty campaign.