Because of the problem with "kill 'em all" spam filters and folks moving around or switching credit cards without thinking to update their eBay registration, I think we'll be seeing more NARU's of the temporary, oversight variety. For example, I had 2 winning bidders recently who won, paid promptly via PayPal, but were NARU'd before I could ship...curiously, both with decent, consistently postive 50 to 100 plus ratings. When I brought this to their attention, they quickly got their eBay registration info updated, and the NARU just as quickly vanished, having little impact on the overall transaction, other than delaying shipment.
So I'm trying not to automatically assume the worst about NARU's--yeah, I know they're serious--a definite red flag--but from my own experience, more often than not everything does get straightened out in a few days. In other words, I wouldn't panic over a NARU'd bidder/buyer unless their FB indicated some other chronic more serious problem.