When you sign up for an account, you acknowledge
that you are over the age of 18.  Therefore, the
buyer is the one liable, not you.  Remember what
happened with all the law suits going around for
music downloads.

The minors are the ones downloading the illegal
music and the PARENTS are the ones being held
responsible because it is THEIR internet provider
and THEIR computer.

The same goes with Ebay.  The account is THEIR
responsibility and THEIR internet, THEIR computer.
 They can't sue you because THEIR kid went against
the Ebay terms.  If the person gives you trouble,
report them to Ebay for breeching the Terms of
Agreement.  If I am not mistaken, their account
could even get suspended.