Also iirc the £16 allowance includes whatever you paid for postage, ie the goods plus p&p mustn’t be more than £16. I believe the allowance is/used to be slighly higher for ‘gifts’ but nevertheless there is always still a rather small maximum value even if it is genuinely little Jimmy’s 8th birthday present all wrapped up in wrapping paper.
USPS international postage has apparently also seen a 20% or so increase this year and a lot of ebay etc sellers are cross at this as its tipped the balance of making smaller orders from them worth the money/time or not.