I used to be scammed many times by bounties that doesn't pay what I work for them project. It is really bad when you hear that you will be not payed for what you were worked for. Maybe the smell of a scam is that when a bounty doesn't updates on a month. My technique about this is that I used to join airdrop first and then if they pay probably they passed on my first test. Also I used to study about the project first and look up what they got.