The trial court erred when it failed to instruct on a good faith belief defense that a broker-dealer license was not required in prosecution for selling securities without such a license. Cole and Robles were convicted of multiple offenses regarding the sale of securities to elderly investors. On appeal, they contended that the convictions for selling securities without a broker-dealer license had to be reversed because on some counts, they did not know these investments were securities. On the remaining counts, they contended that reversal was required because they were not broker-dealers within the statutory definition, and even if they were, there was insufficient evidence. They also challenged instructional errors which reduced the crime to a strict liability offense, deprived them of a mistake of law defense, and eliminated the affirmative defense of a good faith belief that one is exempted from the licensing requirement. The appellate court agreed that the trial court had a sua sponte obligation to instruct the jury that a good faith belief that they were not required to obtain a broker-dealer license was a valid defense to the violations of section 25210. On some of the counts, appellants met their burden of producing evidence that supported a reasonable doubt that they had a good faith belief, therefore the jurors should have been instructed on the prosecution’s burden to prove that they did not have such a good faith belief. The error here was prejudicial because it was reasonably probable that an outcome more favorable might have been reached had the jury been properly instructed, and therefore reversal was required.