We can only block post-payment order processing based on the buyer's name, email address, or Transaction ID; we have no way to block on the basis of a buyer's prior order history.
You might consider downloading your E-junkie Transaction Log to identify buyers who have already purchased too much, then you can add their names and/or emails to your Block Buyers list in E-junkie Dashboard. They would still be able to purchase and pay, but we would not issue them a link or code, so when they contact you about that, you can decide whether to issue them one manually or just refund their payment.