Legal Question in Business Law in California

The laws are many and various depending on the nature and purpose of the loan, the amount lent, the collateral taken, the repayment terms and the interest rate. Note that certain types of lenders are licensed, e.g. pawnbrokers and real-estate lenders. Perhaps the most restrictive laws on what might be called payday lenders are the usury laws, restricting interest on loans made by unlicensed persons to (generally) less than 10%, see Civil Code sections 1912 to 1916-5. However, I suppose most payday lenders have either pawnbroker or real-estate licenses, thus exempting them from most aspect of the usury laws per se. There are many other laws regulating consumer credit, credit cards, automobile loans, and so on.

You would have to be way more specific than that.