Under what circumstances can Google legitimately request proof of traffic sources for your AdSense account?

Google can legitimately request proof of traffic sources for an AdSense account when there is suspected invalid traffic or unusual activity that raises concerns about the legitimacy of the website's traffic. This includes situations where there is a sudden surge in traffic, a disproportionately high click-through rate, or traffic patterns that suggest the use of bots or other artificial means of generating impressions or clicks. Google may also request proof of traffic sources if they suspect that the website is purchasing traffic from unreliable providers or engaging in incentivized traffic schemes. The purpose of requesting this information is to verify that the website's traffic is genuine and comes from legitimate sources, and that the publisher is not engaging in any activities that violate AdSense policies. Publishers are expected to provide documentation that demonstrates the origin of their traffic, such as analytics reports, advertising campaign data, or agreements with traffic partners. Failure to provide satisfactory proof of traffic sources can result in ad serving limitations or account termination.