There have been a couple of posts from sellers with the same issue this year.
Looking at the padlock, it does not have a complete UK hallmark - it is just marked '375'.
All of the details are here -
https://www.ebay.co.uk/help/selling/selling-tools/selling-authenticity-guarantee?id=4644&st=3&pos=3&...
Items need to follow the 'jewellery policy' so follow the link to that from the above page. The relevant part is this:
Rules for metals
- If your item is made from plated, flashed or filled metals, you will need to clearly state this in the title, item specifics and item description, such as "gold-plated silver"
- Platinum, gold and silver items must meet applicable laws for stamping:
- Gold stamps: 9ct, 14ct, 18ct, 22ct
- Silver stamps: Sterling Silver, 925, 958, 999
- Platinum stamps: Plat, Pt, 850Pt, 900Pt, 950Pt, 999Pt
- Palladium stamps: 500Pd, 950Pd, 999Pd
- Items must meet the requirements of the Hallmarking Act 1973 - opens in new window or tab. For more information on hallmarking, please see t...Hallmarking Guidance Notes from the Assay Offices of Great Britain - opens in new window or tab
- To ensure that you meet any obligations under the Hallmarking Act 1973, where applicable, you should add this notice on hallmarks - opens in new window or tab as an image to your listing
- You should ensure that your item complies with all applicable legal requirements related to levels of metals such as nickel, cadmium and lead in items, as well as other poisons and carcinogens prohibited under eBay’s Harzardous materials policy
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