Like bonuses and payouts wagering is not the same at every casino. Each site will set its own rules and regulations for wagering, so do not think what is in effect on one site will be the same on another one. In addition you cannot assume that every site offers a wagering formula for its payouts. Each casino is as individual as two department store chains, so you need to read the provisions of each site before you begin playing.
Another thing with wagering is some casinos may offer it as an option while others use it as their only payout formula. Again, you must look at the terms of service on each site you intend to use in order to ascertain you understand what to expect and how to expect it. If you prefer flat fee payments and the site doesn’t offer that format, you need to cross that casino off your list.