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, I think it is important to invest in a bounty before joining Once you invest, you can understand what the investment place is like. Also when choosing a good grace campaign the bounty manager the team member the ICO rating the bounty should be selected to avoid scams.