Well, it's supposed to be a simple 5% but not necessarily so. New watches yes. Pre-owned and vintage, rightfully speaking should be also 5% but they could also treat it as purchase for parts cannibalisation and that would attract the 10% tax. So you have to get your seller to document the sale invoices without mentioning used parts. For instance, I recently acquired a vintage DD36 with extra parts, and the moment parts were seen in the invoice, it was whacked with the 10% tax for the full amount
But then again, I order watches on a monthly basis and many pieces came in under the radar; so it looked like they go on a sampling basis there.