Should ebay be allowing the sale of used knives. How do they know people are not under age.

[plpmr]

What differential are you using between 'used' and 'new' knives?

[ruby*tuesday]

I presume that you are a Seller not the Buyer?  Knives are generally not allowed to be Sold on Ebay. Other than Cutlery and Letter Openers.

Enter Knives Policy into Help and Contact for full details.

[pixiesen2012]

you have to be over 18 to have an ebay account

ebay also have a  'confirm you are over 18'  for knife sales