It is very difficult to determine a credible reward, some projects may have a good concept and a good team, but after raising a large number of ETH, ICO is a quick way to get ETH, and after getting a lot of money, it may not be motivated to develop a project. In short, I try to find those who do not need too much time to complete the task to sign up for bounty, so maybe they will lose too much time and energy when they encounter a fraud.