  We consider properties of the measurement intensity $\rho$ of a random
variable for which the probability density function represented by the
corresponding Wigner function attains negative values on a part of the domain.
We consider a simple economic interpretation of this problem. This model is
used to present the applicability of the method to the analysis of the negative
probability on markets where there are anomalies in the law of supply and
demand (e.g. Giffen's goods). It turns out that the new conditions to optimize
the intensity $\rho$ require a new strategy. We propose a strategy (so-called
$\grave{a}$ rebours strategy) based on the fixed point method and explore its
effectiveness.
