How profitable are poker rooms for the operators?

Back in 2004-2005 I remember there were a lot of online sports book before Netteller got frozen by the FEDS. Maybe sports book that operated had solvency issues. There were more F rated sportsbook than B+ ones.

So for pokerrooms, are they profitable in general? Or a lot of them lose a bunch of cash due to high operating cost?

How do you check is the one your are playing on solvent or not?