A quote from gov.uk regarding tax-free shopping:
Goods you cannot get a refund for
You cannot get a VAT refund for:
goods you’ve already used in the EU, such as perfume
To me it feels a little ambiguous. It's very easy to tell if you have used a perfume, but how about durable goods that are purchased in a used state?
To simplify, my question is: if I buy a used guitar or a guitar accessory in a shop in London, will I be able to get a tax refund? Is the process somehow differrent?