Do you believe you are not saved unless you never sin?
I believe it is possible to have sinned, repented, be forgiven then possibly gain eternal salvation. I believe that Christ clearly teaches this and teaches what one must obediently believe and do in this regard; however, objectively in but few cases it is almost impossible to discern the fate of another in this regard (not discounting the possibility that an individual may know only himself that he is not a sinner and is holy).
The Catholic Church canonizes saints based upon the teachings of Christ in addition to taking into account objective evidence of the Holy Spirit manifested in certain individuals e.g. miracles. Regarding canonization, the Church looks objectively at all evidence in regard to that which comprised and comprises the life and legacy of an individual after they have passed before declaring them saint.
A person may have gravely sinned repeatedly during his life and still attain eternal salvation; however, no one including the Church could objectively know his fate as there is only One who knows in such a case. Finally, as to saints, if any contrary evidence were to come to light or evidence was found to be lacking -saint 'status' would be removed.