Offer accepted but price increases during checkout

Question

UK buyer and UK seller.  I had an offer accepted of £79 (incl buyer fee) plus shipping of £5.15.  However when I go to checkout the item price increases to £79.62.   This was not done by the seller - they just accepted my offer.  Why the increase?screenshots of offer and checkout below

john1297576 · Accepted Answer

It  is VAT at 20% on the buyer protection fee £3.11.