Here we report on the preparation and structural, magnetic and electrical characterization of BiFeO₃ and Bi_0.9Ca_0.1FeO₃ ceramic multiferroic samples. We suggest that Ca-doping creates oxygen vacancies and destabilizes the BiFeO₃ spiral magnetic structure. We also study resistive switching effects in Bi_0.9Ca_0.1FeO₃ with metallic electrodes, finding that the appearance of the effect is dependant on the fabrication procedure of the metallic electrode. On the basis of these observations, we critically revise some assumptions in currently available models of resistive switching of complex oxides.