  The transfer reaction $^7{\rm Be(d,n)}^8{\rm B}$ is modelled for the recent
low experimental energies using the DWBA. Tests of the validity of the ANC
method for the extraction of the $S_{17}$ astrophysical factor are performed.
  We show that a peripheral assumption is no longer accurate for center of mass
energies greater than approximately 15 MeV. In all cases we found that core
deformation and/or excitation effects to be small as long as the optical
potential for the entrance channel is not strongly surface peaked. Multistep
corrections to the DWBA were found to be small.
  We also emphasize that the lack of knowledge of the optical potentials for
the entrance and outgoing channels induces severe uncertainties in the
extracted $S_{17}$ astrophysical factor.
