At a point the team start given excuses to abide by what they promised to do or stop communicating with the community then I can sense the project is scam. How do you determine a project is gone bad and won't fulfil it promise? What criteria do you use ? or you wait for years thinking all will be well ?
You only need to observe their community. If there is no interaction between members, technical updates, roadmap update regularly, or they just update their bonus or token sale, it is certainly a suspicious project.