The first sign of red flag for a fail signature campaign: the bounty manager is inactive. If you sight them, better left it and stop wasting your time on it anymore. Too much risk for doing all the work and receiving nothing in the end.
For my long years of participating in a bounty campaign, I have seen several bounty managers that update their spreadsheet during the last week of the campaign. Most of them pay so I won't consider it as a red flag for scamming since I also experience an updated sheet and a very active manager but in the end, the campaign does not pay a single cent to its participant. The issue here would be the fairness of evaluation since it isn't real-time.
The only thing a participant can do regarding a lazy bounty manager is to quit and avoid its future projects. You can also make a complaint on the reputation board but I don't know what will be the effect if you do so.