  Some post-common-envelope binaries are binary stars with short periods that
exhibit significant period variations over long observational time spans. These
eclipse timing variations (ETVs) are most likely to be accounted for by the
presence of an unseen massive companion, potentially of planetary or substellar
nature, and the light-travel time (LTT) effect. In this study, our main
objective is to describe the diversity of compatible nontransit companions
around PCEBs and explore the robustness of the solutions by employing tools for
uncertainty estimation. We select the controversial data of the QS Vir binary
star, which previous studies have suggested hosts a planet. We employ a
minimizing strategy, using genetic algorithms to explore the global parameter
space followed by refinement of the solution using the simplex method. We
evaluate errors through the classical MCMC approach and discuss the error range
for parameters. Our results highlight the strong dependence of ETV models for
close binaries on the dataset used, which leads to relatively loose constraints
on the parameters of the unseen companion. We find that the shape of the $O-C$
curve is influenced by the dataset employed. We propose an alternative method
to evaluate errors on the orbital fits based on a grid search surrounding the
best-fit values, obtaining a wider range of plausible solutions that are
compatible with goodness-of-fit statistics. We also analyze how the parameter
solutions are affected by the choice of the dataset, and find that this system
continuously changes the compatible solutions as new data are obtained from
eclipses. The best-fit parameters for QS Vir correspond to a low-mass stellar
companion (57.71 $M_{jup}$ ranging from 40 to 64 $M_{jup}$) on an eccentric
orbit ($e=0.91^{+0.07}_{-0.17}$) with a variety of potential periods ($P =
16.69 ^{+0.47}_{-0.42}$ yr.)
