Sports betting is less deterministic than cards, since odds are set relative to popularity and past statistics. Sports bettors would make money by recognizing when the odds are unrealistic (e.g. popular team is favored too highly) but these markets are efficient. Think of the parimutuel pool as the original crowdsourcing of wisdom.

Yes, you can sometimes find arbitrage opportunities between different bookies. I knew a person who did this for a while, but most online betting has checks against this. Doing it in person is pretty obvious and a great way to get banned.

You can find two bookies with different odds, such that the expected value would be in your favor. I however did work for a company combating this,by alerting the bookies about such opportunities so that they adjusted their odds.