Please be aware that some people have experienced problems with tickets purchased on ebay.
People have got to the adelphi, taken their seats only to have others turn up to sit in them with tickets. People have been asked to leave or pay up for other seats. This is due to the ticket issuers regularly checking ebay to see if 'touts' are selling tickets for profit. If they decide tickets are being purchased for profit they will inform the seller of the tickets that they are cancelling them - however the seller doesnt always cancel the sale!
Please be aware that if you are paying over the ticket price for tickets that you could turn up and find that you do not have a valid ticket and therefore NO seat!
Be sure where you are purchasing your tickets!