'I do not wish to diminish in any way from the importance of guidance given by Woolf J [in the Van Boeckel case] to Customs officers as to how to exercise their best judgment when making assessments. However, when the matter comes to the tribunal, it will be rare that the assessment can justifiably be rejected altogether on the ground of a failure to follow that guidance. The principal concern of the tribunal should be to ensure that the amount of the assessment is fair, taking account not only the commissioners' judgment but any points raised before them by the appellant.'