  The study of the iron-based superconductor FeSe has blossomed with the
availability of high quality single crystals, obtained through
flux/vapor-transport growth techniques below the structural transformation
temperature of its tetragonal phase, T~450 C. Here, we report on the variation
of sample morphology and properties due to small modifications in the growth
conditions. A considerable variation of the superconducting transition
temperature Tc, from 8.8 K to 3 K, which cannot be correlated with the sample
composition, is observed. Instead, we point out a clear correlation between Tc
and disorder, as measured by the residual resistivity ratio. Notably, the
tetragonal-to-orthorhombic structural transition is also found to be quite
strongly disorder dependent (Ts =72 - 90 K), and linearly correlated with Tc.
