Hello tobiasd4, thank you for your reply and for confirming eBay's position with postage disputes. At the time, I was expecting parcels from various sources. When I received the Royal Mail insufficient postage notice, it didn't specify where the parcel was coming from. So unfortunately, I wasn't able to contact the seller. I paid the £3.50 fee because it could have been for a larger, more expensive parcel from a non eBay seller. When the parcel finally arrived, I realised it was the glue sticks from the eBay seller. Luckily, after some further communication with the seller, they have now refunded me the £3.50 insufficient postage fee. I notice the seller has now increased the price of their product, which will hopefully cover the postage and make it more worthwhile for them as a seller. Thanks again for your help.