But I'd been watching this eBay auction for a week and the bid for the nokton f/1.1 lens had gone higher and higher and higher, to about $660 last night. Then just by chance I bumped into a "buy it now" listing for another nokton f/1.1 by another seller for $645.
(1) I'd never seen the f/1.1 nokton sell for this low before, and...
(2) the bidders in the other auction for that nokton had overshot the price for this new listing and none of them had noticed it yet.
(3) the seller had an excellent eBay rating.
So after aching over it for a couple of hours, I jumped on it. I just had to.
The other one eventually sold for $690 in the end.