It’s been sometime since I bought anything at auction and I was surprised to see postage at £3.99 for Royal Mail 48hr tracked. It’s only £3.55 for a small parcel on the Royal Mail online pricing site. I didn’t have the option of another delivery company so I presumed the seller selected just Royal Mail and there are no preferential rates if only 1 delivery option is selected. Am I correct? 
I can’t find anything showing Royal Mail prices in the help pages, but there are prices for other couriers so I can’t check to see if £3.99 is correct.