  We explore how the behavior of galaxy cluster scaling relations are affected
by flux-limited selection biases and intrinsic covariance among observable
properties. Our models presume log-normal covariance between luminosity (L) and
temperature (T) at fixed mass (M), centered on evolving, power-law mean
relations as a function of host halo mass. Selection can mimic evolution; the
\lm and \lt relations from shallow X-ray flux-limited samples will deviate from
mass-limited expectations at nearly all scales while the relations from deep
surveys ($10^{-14} \cgsflux$) become complete, and therefore unbiased, at
masses above $\sims 2 \times 10^{14} \hinv \msol$. We derive expressions for
low-order moments of the luminosity distribution at fixed temperature, and show
that the slope and scatter of the \lt relation observed in flux-limited samples
is sensitive to the assumed \lt correlation coefficient. In addition, \lt
covariance affects the redshift behavior of halo counts and mean luminosity in
a manner that is nearly degenerate with intrinsic population evolution.
