Shoppers are voicing their frustration following a change that caused listings displaying inaccurate size information.
This online marketplace has altered its size classifications for women's and children's garments without notifying all users about the change.
Many shoppers and sellers have taken to social media stating that platform listings now display a different size category versus the original listing due to the recalibration.
The company said the revised method more closely matches comparable marketplaces.
It has advised users to examine their items and manually change the size where appropriate, causing user dissatisfaction.
Earlier, the sizing featured numerical and alphabetical indicators, such as S/8 or M/10.
The updated approach includes a letter and a range such as S/UK 8-10.
With some products, the sizing has been recategorised - for example a size L was formerly size 12 but currently displays as UK 16-18.
A fashion influencer, who creates plus-size fashion videos, explained the modification "makes transactions more difficult".
"Rarely do manufacturers list XL as sizes 20-22," which is what Vinted now does.
Stephanie Gallen, based in Glasgow, said garments she listed featuring size 14 markings were displaying on the service as larger sizing 20-22.
"Should someone sized 20-22 purchase these they will likely be quite upset," she said.
A different user, from Derby, explained she became annoyed by the change as she had to manually change the sizing for "all her products".
"Personally, this is quite irritating, because of my ongoing medical condition and platform income has been essential following partial earnings loss," she said.
The app has more than 100 million members, including 18 million in the UK.
It has proved a popular alternative versus similar marketplaces including eBay and Depop.
This represents another occasion where an unanticipated change to the app has proved unpopular: previously, the service retracted a modification to its shipping options following member complaints.
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