Concentrating solar collectors direct the sunlight towards a focus point or focus line. Relevant parameters are the fidelity of the concentrator with respect to its ideal parabolic shape, its stiffness under wind and gravitational loads, the angular accuracy of the tracking and the solar weighted specular reflectance of the reflector. Additional aspects refer to the long term durability and ease of cleaning of the reflector surface. Solar concentrators require lower geometrical precision than astronomic apparatus. Therefore, more cost effective designs are possible by using up the overall acceptable error budget to a level that collection efficiency of the reflected sun rays is still very efficient. Understanding the impact of the different parameters describing the quality of the concentrator with respect to system performance and cost is necessary for an advanced and efficient concentrator design. DLR has recently developed guidelines to measure the most relevant concentrator characteristics in its qualification center QUARZ. This paper presents the relevant parameters of mirrors for concentrating solar collectors and discusses their economic impact.