hi allison. depending on what you buy and how much it costs, it may attract import tax. This has nothing to do with ebay or paypal and is (i think) levied by hmrc but actually taken from you by royal mail. The seller will have to put a customs form on the parcel stating what is in it and how much it's worth. Please see chrises answer reproduced below from 2009. When you see a little square, substitue a pound sign. His answer is based on cotton clothing.
Import duties vary but most clothing attracts duty at 12%. However the UK is currently imposing a trading sanction against the USA (because the USA is breaking World Trade Organisation rules by illegally subsiding their cotton farmers). That means that cotton-based goods, from the USA, currently attract duty at 27%. (Duty is ignored, though, if it comes to less than �7).
Then there's VAT which is charged, at 15% on both the value of the goods and on top of the duty. (VAT is waived if the value of the goods is less than �18)
Lastly, there's an �8 inspection fee to be paid for examining your goods. (If there's no duty or VAT to be paid, the fee is waived).
Examples. (All are for cotton-based clothing):
1. You buy an item for the equivalent of �15. The duty is theoretically �4.05 but it's waived because it's less than �7. The item is worth less than �18, so there's no VAT to pay. Since there's no duty or VAT, the inspection fee is waived. Amount to be paid to postman, upon delivery = Nil.
2. You buy an item for the equivalent of �20. The duty is theoretically �5.40 but it's waived because it's less than �7. However the item is worth more than �18, so you pay 15% VAT = �3. There's also an �8 inspection fee. Amount to be paid to postman = �11.
3. You buy an item for the equivalent of �30. The duty is �8.10. You're charged VAT on �38.10 (the cost of the item plus the duty) = �5.72. There's an �8 inspection fee. Amount to be paid to the postman = �21