If the seller has one of a kind item such as a used bicycle, then sells it on Craigslist, then it would pointless to jack up the price on E-Bay so it wouldn't also be bought there (and if sold in 2 locations, then the seller can't replace it).
With the battery guy, I don't see any actual sales at the high prices (open up the individual items and click on the number sold).
My guess is that as he sells down his inventory, he jacks up the price until he gets new stock in.
Then he drops the price again and lets the sales resume.
He may also sell using Amazon or a personal web page. However, there is no fraud unless he is offering for sale items that he doesn't actually have in stock.
So,
pick an item that he lists a stock of 1,100 for $5,002.69 each, and put in an order for the full 1,100 of them for a total of $5,502,959.
No doubt you'll have the seller sweating as he scrambles to put together the inventory he sold and doesn't have. But, if he manages to do it, he'll score over $5 Million profit. For that, he may be able to get his shipment as an overnight express delivery from China.