With the emergence of business to business eCommerce conventional trading practices need to be adapted to the new electronic environment. One such trading practice is the call for tender (CFT) which is heavily used for trading perishable goods. A naive translation of the CFT to mediated eCommerce introduces new manipulation possibilities like identity masquerading, repudiation of messages etc. In a first step. we show how the basic CFT can be made robust against these security attacks. However. this approach does not eliminate fundamental economic design problems of the CFT itself. In a second step. we show how the CFT can be protected against attacks that damage the fairness and economic efficiency of a market by turning it into a secure sealed-bid auction protocol.