only thing with the ebay ones is that you may or may not have to purchase a license for the vag-com software. Its hit or miss, but still cheaper either way than buying it on ross-tech. I went ross-tech, but I usually just buy new or dont buy. rarely do i buy used anything. paranoia I guess -shrugs-
If its a true ross-tech cable, and the previous guy deactivated it on his/her computer... then the cable should carry the license and you shouldnt need to pay for it.