Let $\alpha$ and $\beta$ be complex numbers such that $|\beta| = 1$ and $\overline{\alpha} \beta \neq 1.$  Find the maximum value of
\[\left| \frac{\beta - \alpha}{1 - \overline{\alpha} \beta} \right|.\]
Since $|\beta| = 1,$ $|\overline{\beta}| = 1,$ so
\begin{align*}
\left| \frac{\beta - \alpha}{1 - \overline{\alpha} \beta} \right| &= \frac{1}{|\overline{\beta}|} \cdot \left| \frac{\beta - \alpha}{1 - \overline{\alpha} \beta} \right| \\
&= \left| \frac{\beta - \alpha}{\overline{\beta} - \overline{\alpha} \beta \overline{\beta}} \right| \\
&= \left| \frac{\beta - \alpha}{\overline{\beta} - \overline{\alpha} |\beta|^2} \right| \\
&= \left| \frac{\beta - \alpha}{\overline{\beta} - \overline{\alpha}} \right| \\
&= \boxed{1}.
\end{align*}