The growing use of mass customization necessitates an understanding of consumers' evaluations of mass customization platforms. We hypothesize that consumers' objective and subjective knowledge of the customized product moderate the influence of idiosyncratically evaluated (i.e., personalizable) attributes on satisfaction with a customization platform. Consistent with our theoretical framework, results from three experiments show that offering greater variety in idiosyncratically evaluated attribute options increases consumers' satisfaction to a greater extent for: (1) novices than experts (2) consumers with more subjective knowledge, and (3) miscalibrated consumers whose subjective knowledge does not match their objective knowledge, than calibrated consumers whose subjective and objective knowledge match.