I know this one... It's simply a pricing bot algorithm.
Sellers can auto-set their pricing so that their "vgc" book is priced at e.g. 50p above the lowest price book", theory being that the buyer will pay 50p more for their better copy.
Then it's all fine.....unless the other buyer has set their price as "£1 above the Lowest other price" (on the grounds that when two people want to buy the book, theirs will make more). So you get two book priciing systems looking at each other, both looking to increase the price a bit.
So you have three copies of a book: one (non botted) is for 0.01 plus postage.
someone buys the book that's 0.01 plus 2.80 postage.
This leaves our two remaining copies at 0.51 and 1.01. The 51p book then looks at the 1.01 and its bot thinks "ok, I need to be 50p above that one" and increases its price to 1.51.
The 1.01 book then says "ooh, it's gone up! Must be demand. I'll increase again... To 2.51."
The bots then "fake bid" against each other until either someone buys the lower price copy (which may be when it hits almost the new price) or one seller notices the silly price and withdraws it, leaving the other copy stranded at £253.17 for some nursery rhymes.
Aethel, that's a brilliant explanation
. I knew that somewhere in the murky recesses of my brain, I also understood what must be happening here, but even a strong cup of coffee and a long-handled broom were unable to unearth the knowledge
. I shall now file your explanation somewhere - perhaps not 'safe', though.