You won't pay VAT on the price of the secondhand clothing if you buy from UK sellers.
From your own listings, you can see what the buyer will pay and VAT is not added for UK buyers.
VAT at 20% is included in the Buyer Protection Fee which is collected by and paid to Ebay.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)