Yes it really happens all the time ! As a bounty hunter , I already have an experience on promoting scam projects. Our first objective on doing bounties is to make money but  we don't take actions on choosing the right bounty. At first, we can't detect whether the bounties we had joined is scam or not , we can conclude it already when it tooks a long time to work or participate in their community. So , it is better to research first about the project/s before joining.