California Code, Business and Professions Code - BPC § 21604

(a) Any person who buys or sells junk acquired in the conduct of any business other than that of a junk dealer or recycler.

(b) Except as provided in Section 21609.1, those purchases of scrap metal by a junk dealer or recycler when the payment for the scrap metal is by check issued to the company represented as being the owner of the scrap.

(c) Scrap metal purchased or received from another junk dealer or recycler who has recorded, reported, and held the material as required. The purchase or receipt shall also be exempt from further holding or reporting provided that the selling party gives the buyer written assurance of this fact. The seller shall be held responsible for any failure to report or hold.