Can't you just take paypal only, or is the e-check done through paypal?  I'm a little confused, could you state "paypal only" in your auction and if they pay with an e-check just refund the money and tell them you don't accept payment via e-check?  I thought the idea was pretty solid, so much so, that before finding this thread this evening, I had even come up with my own certificate and was pretty much going to copy you!