"1. I'm in for a dime."
"In for a dime, in for a dollar" is the American English version of the British idiom "in for a penny, in for a pound." These idioms mean that if you're going to do something, you should do it all the way. Or, if you're going to lose $0.10 on a gamble, you may as well lose $1.
"2. This is a volume business."
This sentence is not directly related to gambling. Volume businesses only deal in bulk. For example, your local grocery store buys its merchandise from a supply or distribution company. Supply/distribution companies are volume businesses.
"3. He’d collect $500 from the underdog betters and pay out $500 to the favorite betters."
The subject of the sentence will collect $500 in profits from the losers (underdogs in this context) and use the money to pay the winners (favorite betters).
"4. I've been getting so much action on the Yankees."
The Yankees are a baseball team in New York state. Getting action means a lot of people place bets on this team.