Under what circumstances can a small claims case be appealed in CA? Is it only for errors of law?
It seems that in California, a losing defendant may appeal as of right, and obtain a completely new trial in superior court. Only a losing defendant may appeal, except that if the plaintiff was cross-sued and lost s/he may appeal. According to This oficial California Courts page:
When you appeal a small claims judgment, you ask the superior court to change the small claims court judge's decision. You will have another court hearing and must present your case again.
A small claims appeal is a "trial de novo" or "new trial." This means that the case is decided by a new judge from the beginning so you have to present your case all over again. Because this case is in the civil division of the superior court (and NOT in small claims court), you (and the other side) are allowed to bring a lawyer to represent you in the new trial.
In a small claims appeal, a new judge hears all the evidence again and makes a decision. That judge does not know what happened in the first trial, so this new judge looks at everything as if the case was being decided for the first time.