In my previous post a I explained how public bail works.
Private bail bonds also follow two general models. First are bonds for which the defendant puts up cash to guarantee his appearance. When he shows up for court, the cash is returned to him. The second type of private bond is one, which uses commercial bail bonds handled by commercial bail bond agents. In this instance the bail bond agents use surety companies to guarantee to the state that they will pay the bond forfeiture.
Alternatively, property owned by the bail agent is pledged to guarantee the defendant will show up for court as agreed. If the defendant does not show up for court, the bail agent will go get him and bring him to court. For this service the defendant is charged a premium.
In the commercial bail bond case, if a defendant fails to appear, the commercial bail agent knows he may have to pay—thus he has the incentive to go out and either re-arrest, or talk the defendant back to court.