Well, you've got exposures on both sides (and you keep the tiny bit in difference between what you buy at and what you sell at, in aggregate.) I'm not sure how gambling bookies work, but I'm assuming it is very simple principles...arent gambling bookies essentially market makers just like Wall Street market makers?
Yeah, when I started as a trader it was pretty much a given that you'd be interested in poker and sports betting. The "training" would consist of the the senior traders asking you to make markets in just about every imaginable sports event, an after-work poker game, and a good few questions about things that aren't normal bets (how many burgers do you think you could eat?).