The reasoning is these are tested and modded and working stable. Not everyone knows how to mod a card, nor has the time to learn. Also, these cards retail for $359+tax+shipping, in the end you are paying about $450 a card. The ones on eBay are likely used and abused in a hot mining facility and all their thermal paste is melted away resulting in 25-27MH caps. These cards are brand new, none of these cards will be duds when it comes to mining, where on eBay you are kind of taking the chance the card you are getting is a good card.