The store, which raises money for the Otago Community Hospice, had experienced an "atrocious" spate of shoplifting in the past fortnight, supervisor Robyn Elliman said.
"Every day, something has been taken," she said.
The thefts, of one or two items a day, started about the time winter boots and coats were put out.
The stolen items had a value of about $300.
One woman tried on a $50 pair of boots, then walked out of the store wearing them, leaving her shoes behind.
Another haggled with a shop assistant over the price of a coat, before stealing it minutes later.
Other incidents were evident from empty hangers left on racks and clothing price tags left in the changing room.
Mrs Elliman believed it came down to a want, rather than a need, for the thieves.
"You are not stealing from us. You are stealing from dying people at the hospice."
Security systems were too expensive, so regular customers had been asked to keep an eye on other shoppers. The changing room curtain had also been shortened, so staff could monitor cubicle activity.
Presbyterian Support Otago retail manager Chrissy Anderson said thefts from the organisation's three op-shops were "reasonably regular", but staff were vigilant in contacting police about shoplifting incidents.
"Stealing from anywhere is a crime. Stealing from charity, I personally think, is a double-whammy."
St Vincent de Paul Society store manager Ken Fahey said shoplifting occurred sporadically, but was "not an issue" in the shop.
Salvation Army South Dunedin Family Store manager Jane Orbell said "shoplifters will always be there", with about one or two being caught each week.
Shoplifters sometimes found it easier to target second-hand stores as many of them had fewer staff than other retailers. Thieves did not seem to care the stores supported a charity.
