  Accurately determining the black hole mass ($M_\mathrm{BH}$) in active
galactic nuclei (AGN) is crucial to constraining their properties and to
studying their evolution. While direct methods yield reliable measurements of
$M_\mathrm{BH}$ in unobscured type 1 AGN, where the dynamics of stellar or gas
components can be directly observed, only indirect methods can be applied to
the vast majority of heavily absorbed type 2 AGN, which represent most of the
AGN population. Since it is difficult to evaluate the accuracy and precision of
these indirect methods, we utilize the nearby X-ray bright Seyfert galaxy NGC
4151, whose $M_\mathrm{BH}$ has been tightly constrained with several
independent direct methods, as a laboratory to assess the reliability of three
indirect methods that have been applied to obscured AGN. All three, the X-ray
scaling method, the fundamental plane of black hole activity, and the
M-$\sigma$ correlation, yield $M_\mathrm{BH}$ values consistent with those
inferred from direct methods and can therefore be considered accurate. However,
only the X-ray scaling method and the M-$\sigma$ correlation are precise
because the substantial scatter in the fundamental plane of BH activity allows
only for crude estimates. Of the four M-$\sigma$ correlations we used, only the
one from Kormendy and Ho yields a value consistent with the dynamical
estimates. This study suggests that the best approach to estimating the black
hole mass in systems where direct dynamical methods cannot be applied is to
utilize a combination of indirect methods, taking into account their different
ranges of applicability.
