1. You start following people and projects who you know are legit af, for example, uniswap, vitalik, arbitrum, 0x project - you get the point.
I scanned their folllowers and checked if there are big personalities in twitter have followed CowSwap and verify if any other person you have mentioned follows this project as well. Unfortunately, I can't seem to find one of them.
The image and cowswap was an example (but still they are followed by known projects in ethereum - 1inch, balancer, matcha, paraswap, defipulse, gnois,..) . You can check arbitrum they are followed by vitalik, that follow can help you determine the projects legitimacy to some extent.
Sometimes, their follower count increases due to some bounties/ advertisement happening on the grey area of cryptospace. And we can't be certain if those numbers alone will have bearing on the legitimacy of the service unless it is proven by time. This applies to all the projects though..
That's true, that's why you follow people who you know are legit, it's unlikely for them to follow due to bounty or similar.