I've seen the ad for sell your gold on telly. they don't want gold-plated and I'm having a sort-out of old jewellery and some I've inherited,nothing of huge value I'm sure. How can you tell the difference? Not all is hallmarked is it? I have some tiny 9ct gold studs from Samuels for instance which have no marks on them at all.
That will only work if the base metal is magnetic, not all of it is.
If it's not hallmarked, it can't be sold as gold. You would have to send it off to be tested and assayed.
Your gold studs from Samuels are definitely not gold.