Which of the following classifications is NOT a type of billing scheme?

Bid rigging is characterized by a group of competitors agreeing to manipulate the bidding process for contracts, ensuring that specific parties win contracts while circumventing true competition. It primarily occurs in the context of procurement and does not specifically relate to fraudulent billing activities that typically involve manipulation of invoices or payments.

In contrast, the other classifications mentioned involve methods by which individuals or groups submit fraudulent or misleading invoices to misappropriate funds. Shell company schemes involve the creation of fictitious entities to generate invoices for goods or services that were never provided. Personal purchases with company funds represent a misuse of company resources, as individuals could submit invoices for personal expenses disguised as business-related. Invoicing via nonaccomplice vendors involves sending invoices through legitimate businesses that may not be aware of the fraud, making it an effective yet deceptive billing scheme. These activities are directly aligned with common billing schemes that fraud examiners investigate in financial crimes.