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is the UK in 1920s then most towns had Sales Rooms which held an auction weekly/fortnightly/monthly. They would have valuers, not great experts, but a starting point. In the 1920s, as today, antique dealers, unless of the reputable dealing houses, with a licence, were prone to cheat, lie and thieve.
The auctioneers would be reasonably knowledgeable and most of them had the hallmark manual for English silver. All English silver is hallmarked with the date it was made, the maker's name and the office where it was assayed and stamped. This manual is a book readily available in libraries too so your character might start there.
The hallmarks get rubbed at during cleaning so old silver can be hard to date solely from the hallmarks. But the style of the silver tells the date. There were very specific styles and the way makers actually made the silverware is a giveaway.
Copies of ancient silverware are easy to tell as they are hallmarked. Victorians did a lot of very beautiful ones now valuable in their own right. Tampered hallmarks are reasonably easy to detect.