Acting Commander Brad Royce said the police worked closely with second-hand dealers to ensure the property they traded in was legitimate.
"They do this for two very simple reasons," he said. "Firstly, if they don't ensure the property they buy is legitimate, these businesses can become a secondary victim of the theft offence because any property identified as having been stolen is seized and returned to the legitimate owner.
"Secondly, they may be breaking the laws governing their trade, which can attract significant penalties."
Police officers have been conducting random audits on stock at second-hand dealers to identify any stolen property that has been traded.
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A man vandalised a bus while travelling from Midland to Bassendean on Sunday, May 3.
Police say he boarded the bus about 8.30pm at Midland station and took a seat towards the rear of the bus. He used a white/silver marker to tag "SAVER" or similar to the back of the seat in front of him. He then moved across and tagged the top of another seat before getting off the bus at Bassendean train station. Police have released a CCTV image of a young man they believe can help with inquiries.