I've bought basses from the US and Japan over the years from private sellers. When they arrived, I paid Import Duty and VAT on the value of the goods plus the cost of postage. It was all presented to me as one lump sum due, but usually worked out at roughly an additional 25%. There are different thresholds at play, depending on the item being imported, where you might come in under a taxable value but still liable for Import Duty.