The audit strategy for precinct tabulators such as these is not to audit the machines but the actual ballots, which are retained. Upon suspicion (usually this requires a court order, details vary a lot by state) the original ballots, which are retained after the machines tabulate them, can be hand-counted or more practically recounted by independent machines.

Every conceivable election method is vulnerable to some type of fraud, and hand-counting leads to relatively very high unintentional error rates. Post-election audit sampling is a typical practice in many states and should be in all.