And the IRS (or other country's tax authority) would already have been tipped off to the bank deposits and audited them long before they paid cash for a car or a residence. Were the escort to pay using currency, the seller would be required to file a Currency Transaction Report with FinCen (The Financial Crimes Enforcement Network) in the US or the corresponding agency in the UK, EU, Japan, etc. Were they to pay using a cashier's check (or corresponding instrument in another country) a Monetary Instrument Report would be filed.
Just remember - Al Capone was prosecuted for tax evasion.