Comparison between the best-fit values of M_BH (left panel) and Ṁ/Ṁ_Edd (right panel) derived from the MCMC analysis (which includes constraints on the X-ray emission) and the estimates from M25 obtained using the single-epoch method. Given the bimodal posterior distributions found for all objects, the Monte Carlo samples are divided into two groups: low-mass, highly accreting systems (filled data points) and high-mass, almost inactive black holes (empty data points). Each pair of solutions for a given object is represented by a different marker. Data points for the low mass solution are colour-coded according to the ratio between the mean likelihoods obtained for the low-mass and high-mass solutions, where high values (red colours) suggest a preference for the former. The shaded grey regions indicate a deviation of 0.5 dex from the 1:1 relation.