  We examine systematic differences in the derived X-ray properties of galaxy
clusters as reported by three different groups: Vikhlinin et al. (2009a), Mantz
et al. (2010b), and Planck Collaboration (2011b). The sample overlap between
any two pairs of works ranges between 16 to 28 galaxy clusters in common. We
find systematic differences in most reported properties, including the total
cluster mass, M500. The most extreme case is an average 45% \pm 5% difference
in cluster mass between the Planck Collaboration (2011b) and Mantz et al.
(2010b), for clusters at z > 0.13 (averaged over 16 clusters). These mass
differences induce differences in cluster observables defined within an R500
aperture. After accounting for aperture differences, we find very good
agreement in gas mass estimates between the different groups. However, the
soft-band X-ray luminosity, LX, core-excised spectroscopic temperature, TX, and
gas thermal energy, YX = MgasTX display mean differences at the 5%-15% level.
We also find that the low (z \leq 0.13) and high (z \geq 0.13) galaxy cluster
samples in Planck Collaboration (2011b) appear to be systematically different:
the YSZ/YX ratio for these two sub- samples is ln(YSZ/YX) = -0.06 \pm 0.04 and
ln(YSZ/YX) = 0.08 \pm 0.04 for the low and high redshift sub-samples
respectively.
