The answer is not that simple. While actual police reports are not included, information from police reports is included. This is helpful because even though you may not be able to view all the small details of the police report, you still get insight into someone's criminal history, and can see if the person has been charged or convicted of a crime. Criminal history is "public record" so it makes it difficult for someone to hide.
Furthermore, different states have different laws regarding arrest and conviction records. For example, some states limit the amount of time that an arrest or conviction record can appear on a public background check. Sometimes for less serious offenses,it is possible to get a criminal record "expunged." Getting a record "expunged" requires fulfulling certain conditions, and can include probation, and paying court fees.
Just because someone's criminal history does not currently show in public records, it does not mean that they never committed a crime. This is because of the above exceptions. However, the important point is that running a TruthFinder background check still gives you great insight on whether that individual has a history of breaking the law.