Posting this here, as it's useful information about the sale of train tickets.
Found and pointed out by HotUKDeals moderator fordy
fordy:
The sale of all UK train tickets (including Eurostar tickets) by unauthorised persons is not permitted under the railway byelaws, made under Section 129 of the Railways Act 1993. Therefore, unless you are an authorised seller as described below, you may not list train tickets on eBay. In Ireland, the sale of all train tickets (including LUAS and DART tickets) is not permitted under the relevant railway bylaws.
An authorised person means someone acting in the course of his or her duties who is an employee or agent of the relevant train operator, or any other person authorised by the train operator or a person operating any railway assets.