  Within the formalism of relativistic quantum field theory an adequate
framework for the description of two-particle bound states, such as, for
instance, all conventional (i.e., non-exotic) mesons, is provided by the
Poincar\'e-covariant homogeneous Bethe-Salpeter equation. In applications,
however, this approach usually proves to be rather involved, whence it is not
always quite easy to extract the predictions sought. In view of this, a coarse
idea of the bound-state spectrum to be expected might be gained by adhering to
some simplifying approximations - which constitutes an entirely legitimate
first step. The reliability of the insights inferred from the arising simpler
bound-state equation may be straightforwardly examined by taking into account a
couple of rigorous constraints on the obtained discrete spectrum. Application
of these tools is illustrated for popular potentials.
