  The first science image released by the JWST reveals numerous galaxies in the
distant background of the galaxy cluster SMACS J0723.3-7327. Some have claimed
redshifts of up to $z \simeq 20$, challenging standard cosmological models for
structure formation. Here, we present a lens model for SMACS J0723.3-7327
anchored on five spectroscopically-confirmed systems at $1.38 \leq z \leq 2.21$
that are multiply lensed, along with twelve other systems with proposed image
counterparts sharing common colours, spectral energy distributions, and
morphological features, but having unknown redshifts. Constrained only by their
image positions and, where available, redshifts, our lens model correctly
reproduces the positions and correctly predicts the morphologies and relative
brightnesses of all these image counterparts, as well as providing
geometrically-determined redshifts spanning $1.4 \lesssim z \lesssim 6.7$ for
the twelve candidate multiply-lensed galaxies lacking spectroscopic
measurements. From this lens model, we create a lens finder map that defines
regions over which galaxies beyond a certain redshift are predicted to be
multiply lensed. Applying this map to three galaxies claimed to be at $10
\lesssim z \lesssim 20$, we find no image counterparts at locations (with an
uncertainty of $\sim$$0.^{\prime\prime}5$) where they ought to be sufficiently
magnified to be detectable - suggesting instead that these galaxies lie at $z
\lesssim 1.7-3.2$. In lieu of spectroscopy, the creation of reliable lens
finder maps for cluster fields are urgently needed to test and constrain
redshifts inferred from photometry for a rapidly increasing number of candidate
high-$z$ galaxies found with the JWST.
