Actually, the legal effectiveness of an affidavit (notarized) and a sworn declaration signed under penalty of perjury under the laws of the State of California are exactly the same. See California Code of Civil Procedure section 2015.5.
In small claims court, the rules of evidence are more lax than in regular court. I think what is most important for your case is the content of the declaration or affidavit.
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Typically the evidentiary ruling the bench officer, the Judge will make is hearsay. The witness is not present and can not be cross examined.
As mentioned in previous answer the rules of evidence is more relaxed on small claims court.
So is up to the Judge to allow it or not.
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