Fixed matches can be organized in different ways, depending on how professional the operation is.
At the highest level, the organizers handle all the betting themselves, using legitimate betting entities to place large wagers. Players, coaches, referees, and others who have been bribed are usually prohibited from placing bets to avoid drawing unwanted attention. Instead, they receive their payment in agreed-upon cash bribes.
On the other end of the spectrum are fixes where a team simply stops trying to win. In these cases, players, coaches, and staff start betting against themselves. They inform the opposing team and referees, so everyone bets in the same direction and helps influence the outcome. These types of fixes are much easier to detect and more likely to fail, since individuals often have little to lose and may hesitate to make clearly bad plays or calls.
Between these two extremes lie fixes with some level of professional organization, but without the strict discipline and control seen in the most carefully managed schemes.