Finally, there are names for phenomena that eBay would have sellers believe is conspiracy theory thinking. Ed at BuildASkill.com calls it "tap-on-tap-off" visibility, and "rolling-region" visibility. It's when sellers experience surges of sales, or when all of a seller's buyers are from one particular region. Sellers have raised the issue at Town Hall meetings, and it came up again at the recent IMA meeting in March, where eBay yet again denied there was anything to it.
I believe the first time "geo clustering" came up as an issue was after eBay expanded Item numbers from 10 to 12 digits in 2006.
For those who experience it, it has to be reassuring to know there's a name for it and that they are not alone.