if you trust random accounts you will loose all your Circles!!
At the core of Circles is trust. Trust that other people will not abuse the system. What that means exactly is not easy to define and the social norms of Cirlces will develop over time and also potentially will be different in different communities.
But one thing should be ensured at all times: only humans should receive Circles and each human should only have one Circles account. So in general the minimum requirement for veryfing someone is being convinced that they are
a) a human
b) you should have a good reason to believe that they don’t try to cheat (create multiple accounts)
So you should have met the other side ideally in person and generally assume they are trustworthy.
- What are the consequences if I just trust everyone?
You will very likely loose all your Circles and end up with Circles that no one else wants. For this it is important to understand that not all Circles are equal. In fact - every person issues their own, personalized Circles. If you are trusting someone you are basically saying: their Circles are as good as yours, or technically: you are always willing to exchange their Circles against yours.
Now, a few bad actors are enough to bring you in trouble if you trust too many people. They might create hunderts of accounts (all trusting each other) - as soon as you trust them, they can exchange the Circles from these fake accounts against yours. They will not have any attention to offer anything for those fake-Circles. So you will end of with Circles that no one else accepts and that are thus completely worthless.
You can read more here: https://handbook.joincircles.net/about/whitepaper.html
Finally - what I mentioned here should be the MINIMUM REQUIREMENT to trust someone. Potentially you want to be more strict? Is the person actually willing to offer things they have to offer for Circles? Circles will only work if giving and taking finds a balance. Ideally Circles will at one point be a true Universal Basic Income that allows anyone to receive unconditionally. But every UBI needs to be supported by a wider community that also has members that are able and willing to give more than they take.