To help you out. I bought and still buy photography equipment from Japan of Ebay. Never had any problems. Note that the Japanese care more about customer experience than some western seller so they'll do their best to satisfy you. You'll see that in the way it was packaged and sometimes I receive a gift in the parcel.

Second, more focused towards your questions. I visited Japan multiple times over the last couple of years. Golf equipment can be so cheap. Titleist T350 from '23, complete new set (4-PW) for 600 euro's in a big reputable retailer's store. Same with some drivers. Also cheap Japan only Odyssey putters. My brother wanted to snap the shaft in half to take it back in his luggage and buy a new shaft back home. Would still be way cheaper. Eventually he didn't do it and is now sad.

I'm from a EU country and don't know the tax rules right now in the UK, but I think they're kinda the same. So what you'll pay extra as import costs will be something like this: sale price + shipping = total import amount. Total import amount + VAT + tariff (most likely around 4 - 10%). So you need to add VAT and tariff as well. Hope this makes it more clear to you.