How do I find out if they are genuine
You can't find out whether a buyer is genuine.
You can do the obvious and check their feedback (also the feedback they leave for other users) but this can never 100% reliable. eBay doesn't allow sellers to leave anything except positive feedback and comments, so for all you know the buyer may have built up enough good feedback to scam other sellers who are unable even to mention this.
For a close to £2k gold item you are certainly in the league where you need to anticipate attempts at fraud. eBay has removed most of the protections for sellers which once existed. For example, you are no longer allowed to ask for cash on collection; all items must be won and paid for through eBay checkout. This means that you don't even know how the buyer has paid, so there is always the potential for a credit card chargeback weeks or even months later. Or, or course, for a fraudulent return under eBay's money back guarantee.
eBay no longer allows private sellers to provide contact details to inspect the item until after the listing has ended. This is to ensure that buyers can pay in a way that is covered by eBay's money back guarantee, and to prevent evasion of eBay's selling or buyer potection fees.
