  We derive certain identities satisfied by the left/right-reflection and
transmission amplitudes, $R^{l/r}(k)$ and $T(k)$, of general ${\cal
PT}$-symmetric scattering potentials. We use these identities to give a general
proof of the relations, $|T(-k)|=|T(k)|$ and $|R^r(-k)|=|R^l(k)|$, conjectured
in [Z. Ahmed, J. Phys. A 45 (2012) 032004], establish the generalized unitarity
relation: $R^{l/r}(k)R^{l/r}(-k)+|T(k)|^2=1$, and show that it is a common
property of both real and complex ${\cal PT}$-symmetric potentials. The same
holds for $T(-k)=T(k)^*$ and $|R^r(-k)|=|R^l(k)|$.
