The present invention provides a comprehensive, integrated, computerized system for facilitating transactions in goods or services. The system is capable of facilitating transactions from early or initial stages, such as an electronically proposed purchase order, through to later or final stages, such as payment on an invoice or invoices relating to the transaction. The system is integrated to include the participation of various providers of services ancillary to transactions, such as guarantors, insurers, and shippers.The system may allow sellers or buyers to electronically propose amendments and counter-amendments to, and to amend, through mutual agreement, a purchase order agreement. Any amendments are accounted for in later stages of the transaction facilitated by the system. The system may monitor, utilizing stored transaction information, present and anticipated future credit exposures of buyers, and utilizes the buyer credit exposure information for purposes including facilitating providing buyer credit assurance to sellers. The system may facilitate sellers obtaining financing or advance payment relating to transactions. The system may provide opportunities for sellers or buyers to obtain cargo insurance on goods or services shipped in accordance with transactions.