As ashes tickets are going for alot of money some people are in my opinion trying to sell tickets that don't exsist. I have emailed some people before bidding if I thought them to be dodgy. All but 1 were very respectable sellers. But when I asked a few sellers to provide photo proof of the tickets, 1 of the sellers wouldn't until I have won item. So I stayed well clear of him. So, if you suspect a dodgy seller I think emailing them before bidding with a few questions is a good idea. Usually, not always. But, usually you will be able to tell the good sellers as they will mostly reply and won't mind providing any kind of evidence. Also, try to deal with ebayers with top score when bidding for expensive items. That way you are less at risk.
Good luck if trying for tickets