Loose coupling is often cited as a defining characteristic of service-oriented architectures. Interactions between services take place via messages in an asynchronous environment where communication and processing delays can be unpredictable; further, interacting parties are not required to be on-line at the same time. Despite loose coupling, many service interactions have timing and validation constraints. For example, business interactions that take place using RosettaNet partner interface processes (PIPs) such as request price and availability, request purchase order, notify of invoice, etc. have to meet several timing and message validation constraints. A failure to deliver a valid message within its time constraint could cause mutually conflicting views of an interaction. For example, one party can regard it as timely whilst the other party regards it as untimely, leading to application level inconsistencies. The paper describes how business interactions, such as PIPs can be wrapped by simple handshake synchronisation protocols to provide bilateral consistency, thereby simplifying the task of coordinating peer-to-peer business processes.