Unregulated parks are allowed to police their own accidents, which presents a blatant conflict of interest. Amusement Ride Licensing and Inspection Regulatory agencies set requirements regarding inspection of amusement rides. How often rides are inspected, and by whom, varies from state to state. Some states employ their own inspectors. Some states require parks and carnivals to purchase liability insurance, and rely on the insurance companies to send out inspectors.
Some states allow any person meeting the certification criteria to perform the inspection.
Independent inspections reduce the likelihood of accidents by providing an fresh set of eyes to spot problems before accidents occur. They complement the inspection and maintenance procedures implemented by the parks. It's quite common for used amusement rides to be sold off, just as you might sell your car or your washing machine. Manufacturer's updates aren't always forwarded to the new owner. Part of an inspector's job is making sure that amusement ride owners have the latest safety information regarding the rides they operate.