Sellers looking to maximize profit but expecting would-be buyers to haggle may conversely make a "high-ball" offer and/or asking price.
If a person is already enjoying the prospect of an excellent deal and the future benefits of the item or idea, then backing out would create cognitive dissonance, which is prevented by playing down the negative effect of the "extra" costs.
It is most common in situations where the tax authorities reasonably expect taxable income to exist but cannot, without the taxpayer's cooperation, independently determine the amount for want of any reliable paper trail and/or other documentation.
Unless the taxpayer has failed to disclose anything at all (or declared an unrealistically low figure), then without reliable documentation to prove any suspicions tax authorities and the governments they serve face a dilemma – they can either choose not to pursue their suspicions or they can employ highly subjective and/or arbitrary enforcement methods (such as so-called "lifestyle audits") to provide legal basis to their claims.
Even absent such rigorous and targeted recordkeeping requirements, the increasing prevalence of tipping using electronic payment methods makes it far easier today for tax authorities to obtain credible evidence of low-balling compared to past years.
In response, tax authorities suspecting such activities sometimes forgo criminal charges in favor of civil proceedings since these have a much lower standard of proof.