Under what circumstances will appellate courts find error in a case where a defendant pleaded guilty in return for a reduced sentence?

below is itself subject to an exception: Where the defendants have pleaded guilty in return for a specified sentence, appellate courts will not find error even though the trial court acted in excess of jurisdiction in reaching that figure, so long as the trial court did not lack fundamental jurisdiction. The rationale behind this policy is that defendants who have received the benefit of their bargain should not be allowed to trifle with the courts by attempting to better the bargain through the appellate process." (People v. Hester (2000) 22 Cal.4th 290, 295; People v. Couch (1996) 48 Cal.App.4th 1053, 1057 ["When a defendant maintains that the trial court's sentence violates rules which would have required the imposition of a more lenient sentence, yet the defendant avoided a potentially harsher sentence by entering into the plea bargain, it may be implied that the defendant waived any rights under such rules by choosing to accept the plea bargain"].)