I think you can either apply a case study with a real data and compare the model results with the actual performance of the system or you can use a data set from the literature and compare the model results with too. Both of them will make you able to judge the validity of the model. You can find to what extend the model results are justifiable, explainable and close to the real case measurements.
Design your simulation so the Key Performance Parameters (KPPs) and Measures of Effectiveness (MOEs) are easily measurable. See my paper on RG "Simulation-Based Engineering of Complex Systems" that discusses your problem.
Further, I recommend a first, quick plausibility check of the outcome measurements straight after the simulation runs and before the more systematic methods like Monte Carlo Simulation.
Does the throughput, WIP, waiting time sound reasonable?
It might require some experience to check the plausibility of these measurements in accordance to the input variables, but in most case common sense gives already a good answer.