A Woolworths customer has been slammed on social media after claiming to witness a man shoplifting an expensive item and doing nothing.

The woman in Tasmania has claimed to witness a male shopper scan the 15c grocery bags that were over an expensive pack of smoked salmon before moving through the checkout.

The act concealed the expensive salmon from the staff.

“Yesterday I was at Woolworths and I watched a man very carefully put a bag of packed groceries over what appeared to be smoked salmon (gold vacuum sealed ‘trays’ anyway) in his trolley at the checkout,” she said.

“The man left the store without anyone checking his trolley.”

“He knew quite well there were things left in the trolley, why else would he have been quite so pedantic about the bag placement?”

After posting it on social media, she was slammed for "dobbing" on the shopper as well as not stopping the man.

“Why didn’t you say something to the man? You should’ve approached him or called the police,” said one.

Said another: “Why didn’t you say anything to the man? Something simple like, ‘Hey Mate, what about the salmon under the groceries?’"