[gamblor956]

The IRS doesn't have a system to track down FB posts or Instagram photos. It doesn't even have the resources to maintain its own systems.

Audits are randomly chosen out of several pools (i.e., corporations, very wealthy individuals, the self-employed, business-owners, every else, etc.) with heavy emphasis on high-fraud pools such as the self-employed. These pools are generated based on self-reported information (the much vaunted/feared comparative reporting analysis system is years from implementation). Due to high fraud levels, some pools (i.e., the self-employed pool) have higher likelihoods of audits but from the standpoint of the taxpayer, the increased risk is isn't meaningfully worse.