Unless you have IPR (instant payment required) option on your listing then buyers basically have 8 days to pay.

I don't think the buyer opts to make payment by eCheck and I'm not sure all buyers are even aware that their transaction will be made via eCheck at the time they bid/buy.

I believe PayPal uses the eCheck if the buyer doesn't have ample funds in their PayPal account at the time of purchase and has not backed up their account with a credit card.

So...not really sure you can enforce a "No eCheck" stipulation since PayPal determines when an eCheck is used.

Echecks are not always a bad thing. I've sold several items by eCheck and never had a problem