What tweaked my interest was the combination of "reasonable assurance" and "non-revocable". Meaning that if a registration request is processed for a registrant, that the registrar is required to take money for it at some point. Simply deleting the transaction and telling ICANN "oh, we didn't really want those 4 million registrations" doesn't appear to be an option from my read - there was never a "reasonable assurance"
Let's say I want to do domain tasting. On each daty of the month, I register 100K domains. Starting on the sixth, each I delete all of the domains I registered five days earlier before I register the 100K new domains. (We'll ignore the 73 domains a day that I decide to keep.) In a steady state, I'm registering and deleting 3 million (100K x 30) domains a month, but I never have more than 500K registered at once. So long as I have provided the registrar with a letter of credit to cover the cost of 500K domains, I'm all hunky dory. I believe this is basically the same way that the money flows from registrars to registries. If nothing else, this tells me that unless a registrar keeps its books unusually incompetently, nothing short of a full CPA style audit of each day's status of adds, deletes, payments, and outstanding credit will show whether the registrar is beyond its payment assurances, and even if there is, if it's only by a little bit a registrar could plausibly argue that it was a harmless mistake. The other reason I doubt that you'll find registrars adding large numbers of unpaid domains is that they are in the same situation with the registries, so they'd be putting their own real money at risk. R's, John