  There are some indications from recent determinations of the strong coupling
constant alpha_s and the gluon condensate that the Operator Product Expansion
may not be accurate enough to describe non-perturbative effects in hadronic tau
decays. This breakdown of the Operator Product Expansion is usually referred to
as being due to ``Duality Violations.'' With the help of a physically motivated
model, we investigate these duality violations. Based on this model, we argue
how they may introduce a non-negligible systematic error in the current
analysis, which employs finite-energy sum rules with pinched weights. In
particular, this systematic effect might affect the precision determination of
alpha_s from tau decays. With a view to a possible future application to real
data, we present an alternative method for determining the OPE coefficients
that might help estimating, and possibly even reducing, this systematic error.
