The man allegedly attempted to leave both shops on April 29 with a carton of alcoholic drinks without paying.
In each case, he was confronted by a staff member, before allegedly saying he was armed with a knife and warning the employee to stay away.
The first incident occurred at 1.15pm in a North Beach Road bottle shop in Gwelup, and the second in a store on Ellen Stirling Boulevard, Innaloo.
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READ NOW“After the incident in Innaloo, a customer at the shop noted the details of a vehicle the offender left the scene in,” Detective First Class Constable Karen Higgs said.
“Acting on that information, a search warrant was executed in Clarkson and a 20-year-old man was arrested.
“Unfortunately, the member of the public left the shop and didn’t leave their details.
“We would be very interested to speak to that person and we ask that they come forward and contact us.”
As well as the armed robberies, the man was also charged with breach of bail.
Anyone with information can call Crime Stoppers on 1800 333 000 or report online at www.crimestopperswa.com.au.