Elderly woman injured after online sale goes wrong, leaving $3000 gold chain missing

An elderly woman has been badly injured in a Facebook Marketplace sale that went horribly wrong.

The Swan View woman, in hers 80s, and her partner James were trying to sell an antique necklace worth thousands of dollars but now they're warning others of the dangers of selling to strangers online.

James still in shock after what was meant to be a simple online sale left the 84-year-old's partner injured and a $3000 gold chain missing.

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"Bashed her mouth, broke her tooth, black eye, bleeding, bleeding everywhere," James told 9News.

The elderly couple travelled to Rockingham after being given a fake address by a man wanting to buy the gold chain.

"He just grabbed it in his hand and ran towards his car," James told 9News.

James' partner desperately tried to stop the man and was dragged by the car door, with neighbours on Bell Street rushing out to help.

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"We could see her laying on the road," Stephen Spiers told 9News.

"So we knew somebody was in trouble and raced straight out to help her."

James' partner was hospitalised but is now recovering at home.

The pendant remains missing, believed to have been dumped near Bell Street and Griggs Way.

"We believe the accused has thrown the pendant from the vehicle and we are asking members of the public to be able to look out," Kathryn Hicks from WA Police said.

A 31-year-old Rockingham man has been charged with aggravated robbery and possessing prohibited drugs.

He's set to face Perth Magistrates Court in March.

Anyone with information or that locates the jewellery is asked to call Crime Stoppers on 1800 333 000.