You are right, no matter how big the exchange is, it is always open to scams, I don't see the negative side of having a WhatsApp group, I am a technology man, and I can't do anything to earn your trust, this is when I want to ask you, what can I do to have it? I am not interested in wealth, I want to leave my mark on the world and I can do it with cryptocurrencies.
That's why I don't charge for this service for now, I want to give the users what they want and I as a user want this
Most people will not just put money into a random platform that claims to be an exchange. They will prefer to use big or popular exchanges regardless of the high fees. Many good businesses indeed started small but they did a whole lot of work to gain customers trust. Mere words will not make you trustworthy because scammers also come up with convincing words.
You have started well by trying to build a community but you need to do more. If you claim that your service is decentralized then there should be an escrow system put in place and a trusted arbitrator in case of dispute during the exchange process. You also need to do a lot of publicity to attract more users this is because liquidity is very important. If customers observe that they experience difficulty in getting trade deals, they might not continue using the platform. I watched the video and it is only in a single language. If you are considering to build a global brand, you have to include more popular languages.