People use the automatic pricing software, I'm not sure exactly how it is supposed to work. It's designed to create prices slightly lower or higher than some reference I think. Sometimes it runs away and creates absurdly high or absurdly low prices.
There are often prices on ebay for stuff that is 100x it's usual selling price, these are for common things where there is no shortage of supply. I don't think anyone is expecting someone to accidentally pay £900 instead of £9, they just don't have time to monitor 1000's of prices if the pricing algorithm goes wrong.
Yes, called repricing software.
If you keep stuff in your Amazon cart and when you log in after a time and see a bunch of stuff in your cart changed price, often by a very small amount, that is vendors using repricing software.
They have different settings and options depending on the specific software, but you can use it to ensure you are the lowest priced seller down to a certain price, or to ensure that you always sell for MSRP + 1% or something.
I wish Amazon would ban the use of repricers, because I think it leaves a bad impression upon the customer when they log in and see lots of items in their cart have changed price by a few pennies up to several dollars or more. It makes the customer feel they are being gouged on price, and/or encourages them to not purchase until they see the price go down.
At christmas, my brother wanted some kind of baby walker for his son. I looked on Amazon and I thought I saw them for $39. When I went to buy it a few hours later, the price went up to $69... but everyone was out of stock so I figured I made a mistake. Then I saw another vendor selling it for $49, so I bought it from them and returned the first one (at no cost to me). Then I saw Amazon got them in stock and was selling them for $39 fulfilled by Amazon (and both sellers had dropped their price back to $39), so I bought one from Amazon and returned the other one to the $49 seller. I made sure to ship them back on the last day of my return window so that the sellers would be out of that stock for the longest time possible. Yeah, a dick move... but so is jacking the price up opportunistically.