all BTC exchange rates are calculated using the actual bitcoin exchange sites. They used to be displayed on the front page of the site, however there can be some security flaws with integrating a clearnet API into a hidden service (obviously), so that was scrapped a while back. The exchange rate is not arbitrary. Take the price of an item and go to one of the major exchanges and stack it up against the current exchange - it will be close, a little higher because of listing fees.The algo for calculating the exchange rate for the site uses a rolling, front-weighted 24 hours moving average to level out major spikes if a big buy or sell order goes off on the exchanges and pushes the price one way or the other. It is more than fair.I think you should do some way more serious research into what's going on here before you come out with a post like that. It is better to ask questions than come in with "I know it all, and here's how it should be, even though I just got here." I've been here for over a year.