  The inclination angle of substructures in active galaxies gives insights into
physical components from scales of the vicinity of the central black hole to
the entire host galaxy. We use the self-consistent reflection spectral model
\textsc{RELXILL} to measure the inclination of the inner region of accretion
disks with broadband ($0.3-78\,\rm keV$) X-ray observations, systematically
studying the reliability of this methodology. To test the capability of the
model to return statistically consistent results, we analyze multi-epoch, joint
XMM-Newton and NuSTAR data of the narrow-line Seyfert~1 galaxy I\,Zwicky\,1 and
the broad-line radio galaxy 3C\,382, which exhibit different degrees of
spectral complexity and reflection features. As expected, we find that adding
more data for analysis narrows the confidence interval and that multi-epoch,
joint observations return optimal measurements; however, even single-epoch data
can be well-fitted if the reflection component is sufficiently dominant. Mock
spectra are used to test the capability of \textsc{RELXILL} to recover input
parameters from typical single-epoch, joint observations. We find that
inclination is well-recovered at 90\% confidence, with improved constraints at
higher reflection fraction and higher inclination. Higher iron abundance and
corona temperature tighten the constraints as well, but the effect is not as
significant as a higher reflection fraction. The spin, however, have little
effect in reflection-based inclination measurements. We conclude that broadband
reflection spectroscopy can reliably measure inner accretion disk inclination.
