When an item has sold but the seller changes their mind about selling it, eBay still charges them fees for the sale. These will be refunded if thes seller provides an acceptable reason, for example that the buyer asked to cance the sale.
As you have discovered, some sellers lie to eBay in in order to get their fee refund. This is reportable to eBay, which will that it seriously as the seller has not only refused to honour the sale, but is also dishonestly trying to evade payment of their fees. See:
Report issue with seller: https://www.ebay.co.uk/help/buying/resolving-issues-sellers/report-issue-seller?id=4022&st=12&pos=1&...