Growing operational complexity and higher variety of products require flexibility in assembly. Despite its many benefits flexibility is a complex concept that requires evaluation to harness its full potential. This study uses virtual verification tools as enablers of the decision making process for production system design of a flexible multi-product assembly system. A case study approach analyses a flexible assembly concept for the earth moving equipment industry through a visual and a discrete event simulation model. The paper also discusses the challenges faced by virtual verification tools when applied to the evaluation of flexible assembly systems.