Phase Measuring Deflectometry is a highly precise and full-field measurement technique suitable for specular surfaces. Typically, computer displays are used to provide reference patterns whose distortions, when observed as reflections at the surface under test, provide the information to determine its shape. During the evaluation, an ideal display is usually assumed, ignoring properties like shape deviation with respect to a plane. Such deviations, however, limit the accuracy of this technique. To provide a starting point for the development of a more sophisticated evaluation technique, this paper presents our models and results for the simulation of non-ideal display properties in deflectometry. Our simulations contain the geometrical calibration of components of our setup as well as the shape measurement. Evaluations are based on global deviations of the measured surface. The display properties under consideration are investigated individually as well as in combination. As a result of our model-based investigation, we find that shape deviations of the display are the most dominant influence when measuring the global shape of the surface under test while the influence of angle-dependent emission characteristics of the display is neglectable.