Wow ! Countersports is greaaaaat ! I was waiting that from a long time

But who is behind ? Because we need to trust the feed issuer.
That looks like betfair without betfair, really good job
Who we need to trust? Yourself so you dont play or offer too small or big odds

If i have understand right how that working?
You have to trust the feed issuer. But he has nothing to win by rigging an outcome (maybe just a one time gain on a strong bet), because that would basically be the end of his business.
So basically yes, this is a nice step forward !