  We establish restrictions on $B \ra K ( K^* )$ form factors imposed by recent
data on $B \ra J/\Psi + K ( K^* ) $ decay rates and polarization. We show that
these constraints are not satisfied by few commonly used models. Finally, we
relate $B \ra K ( K^* )$ form factors to those in $D \ra K ( K^* )$ transitions
using the heavy flavour symmetry as proposed by Isgur and Wise and discuss the
uncertainties in this procedure. We find that this method also leads to form
factors excluded by data.
