There are many sources of unintentional tampering:
Can you tell the difference between normal diurnal fluctuations and someone sleeping with a window open? Unintentional interference is no excuse to allow an invalid measurement to be presented to a client. All of the topics you have previously reviewed can help you identify and prevent interference. However when the data appears to have been tampered with intentionally or not, you simply have to ask. Figure 10 is the result of a measurement with a homeowner that slept with a window cracked open. This was discovered after we asked the homeowner if they maintained closed building conditions, and verified EVERY window was shut.