Article 220(2)(b) of Council Regulation (EEC) No 2913/92 must be interpreted as meaning that an importer may not rely on a legitimate expectation, in accordance with that provision, in order to object to a post-clearance incurring of liability for import duties, submitting that he acted in good faith, unless three cumulative conditions are met. It is necessary, first of all, that those duties were not levied as a result of an error on the part of the competent authorities themselves, secondly, that that error was such that it could not reasonably have been detected by a person liable for payment acting in good faith and, finally, that that person complied with all the provisions laid down by the legislation in force as regards his customs declaration. Such a legitimate expectation is lacking, in particular, where, although there are clear reasons for doubting the accuracy of a Form A certificate of origin, an importer failed to obtain, using his best efforts, information concerning the circumstances of the issue of that certificate in order to verify whether those doubts were well founded. Such an obligation does not however mean that an importer is required, in general, to systematically verify the circumstances of the issue, by the customs authorities of the exporting country, of a Form A certificate of origin. It is for the referring court to determine, taking into account all of the specific facts of the dispute in the main proceedings, whether those three conditions are met in this case.