1. A transaction payment system to audit transaction data for a multitude of different transaction parties as a function of contract terms agreed to by a buyer of merchant offerings and a seller of the merchant offerings for each transaction, the system comprising: a data-storing memory circuit storing the agreed-to contract terms and data element specific classification rules, a software-programmed circuit configured, for each of a multitude of sets of transaction data, to respond to activity involving a transaction for at least two of the parties, by accessing the memory circuit and retrieving stored data therein for the transaction; execute an identification process, using the retrieved transaction data, to identify selected ones of the data element-specific classification rules pertaining to the transaction parties; select one of a plurality of data-auditing processes respectively programmed on behalf of disparate entities; execute the selected data-auditing process to audit individual data elements within the transaction data set using the retrieved transaction data and the identified data element-specific classification rules as inputs to the process to determine a condition of electronic payment data validation for each data element.