There could be an overriding PL Rule (30 days) where a deadbeat buyer/seller gets nominated.
There could also then be a Stated Rules in Each Unique Sales Thread Rule where, whatever the seller states to be his/her rules, the seller is free to relist items if the buyer does not pay within the stated time frame but the buyer cannot be nominated for the PL.
The problem with this, of course, is that some buyers will inevitably click the I'll Take It, change their mind, and just wait out the seller's time frame without fear of the PL. However, the seller would know to cut that buyer out of future transactions and, when relisting the item, could state something like, "Item relisted due to non-payment".