Since I've been tagged by OP I'll chime in, but I am not going to get sucked in to the back and forth drama.
In terms of the actual case:
There was a similar case a few weeks ago with bitcasino.io, where a user was not allowed to withdraw his winnings, and bitcasino.io stated that the user was using multiple accounts. They clearly spelt out their reasoning behind this statement in this post:
https://bitcointalk.org/index.php?topic=5260832.msg54754514#msg54754514. They also said something quite relevant to this case:
We know however that our community here requires something more tangible than simply our word.
Given that Bitcasino.io and Sportsbet.io are owned by the same company, I see no reason why one arm would be willing to spell out how they came to a match, while the other says they cannot expose their methodology.
As far as I am concerned, although I do not believe Sportsbet.io are scammers in this situation based on the evidence presented so far, it does not paint them in a good light that they are unwilling to offer any proof for their side of the story.
In terms of LFC_Bitcoin:
I did not receive any PM, and I have not seen its contents, but from what I can surmise based on this thread, then I have no issue with it.
DT selection is meant to be affected by user lists, and it is totally legitimate to try to honestly convince other (real) people to use a list more in-line with your views.
Given what theymos has said here, coupled with the fact that theymos himself sent out PMs asking other users to excluded a user from their trust lists, I see no issue with sending a PM asking other users to review a flag.