  Motivated by the problem of characterizing KMS states on the reduced
C$^*$-algebras of \'etale groupoids, we show that the reduced norm on these
algebras induces a C$^*$-norm on the group algebras of the isotropy groups.
This C$^*$-norm coincides with the reduced norm for the transformation
groupoids, but, as follows from examples of Higson-Lafforgue-Skandalis, it can
be exotic already for groupoids of germs associated with group actions. We show
that the norm is still the reduced one for some classes of graded groupoids, in
particular, for the groupoids associated with partial actions of groups and the
semidirect products of exact groups and groupoids with amenable isotropy
groups.
