As planned, I made a large bid shortly before the end, then alerted Ebay that I bought it to prevent fraud. For several hours I was really sweating, because when the dust settled the runner-up bid was also very large and apparently a genuine one (an odd amount, $2666.60), and I feared that Nassar would send a 2nd chance offer to that bidder.
A risky strategy, but it worked out ok in the end :
The other item listed by ID evinty0, a fake double overprint, also seems to have vanished. But even though I sent them cast-iron proof of the counterfeit 2/6d OS overprint (before & after photos, plus the previous purchase listing number) it appears that they have not NARUd the account, which is puzzling.