I buy a fair bit from eBay/the states
Their shipping charges are stupidly expensive (but this is down to American shipping costs not eBay). If the seller chooses to go through the global scheme then import charges are automatically applied at checkout, yes they are high (I need to look in to whether they are higher than HMRC charge) but it means you have paid the charges so there should be no delay nor any fees to pay once your item arrives in the UK.
I certainly would not recommend asking the seller (before you purchase) to amend their listing so they don’t chose the global scheme then asking them to mark item as a gift. No way.