I imagine I would trust a Head-fi user to sell quality use equipment over an anonymous ebayer, but I doubt I'd find a t1 at this price-point.
Is it $750USD? I am assuming you are from America, I am from Australia and currently there is a ad on Gumtree for T1's. The price is $800AUD (634USD) negotiable. I don't know if you want to buy international or not or if he's willing to sell them but I would put more trust in him then a anonymous eBay seller.
http://www.gumtree.com.au/s-ad/campsie/headphones-earphones/beyerdynamic-t1-up-for-sale-best-headphone-for-audiophile-/1077943090