The only way that Ebay allow their sellers to verify age to buy bladed items is if the buyer can pay with a credit card.
I suppose if somebody else used your credit card because they are under 18, you would find out.
If somebody 'borrows' your driving license you would never know.
Is there somebody you know with a credit card who would pay if you reimbursed them?
"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)