  There is an increasing amount of literature concerning electronic properties
of graphene close to the neutrality point. Many experiments continue using the
two-probe geometry or invasive contacts or do not control samples' macroscopic
homogeneity. We believe that it is helpful to point out some problems related
to such measurements. By using experimental examples, we illustrate that the
charge inhomogeneity induced by spurious chemical doping or metal contacts can
lead to large systematic errors in assessing graphene's transport properties
and, in particular, its minimal conductivity. The problems are most severe in
the case of two-probe measurements where the contact resistance is found to
strongly vary as a function of gate voltage.
