Just got into options and one thing I'm wondering is it legal for the writers/large trading firms to use their knowledge of options made through them (or from knowledge from other trading firms) to bet against, thus making the option fail. Or to use the same knowledge and buy before a large option expires to perhaps benefit from the positive effect on the market of said option. (I'd imagine this would have to be a large amount of people/money betting options at the same time or cloes to on a particular stock).