This is a great opportunity, by the way, so you should get yourself a copy. The combination of being wrong about 30 seconds after publishing and so many people using it gives you a chance to profit.
When you are a little more experienced, you can check this unnamed document to work out which items are being under or overpriced and you suddenly have two prices for each item. This happens in real stock trading; you buy from the person selling cheapest and sell to the person paying the most.
Don’t feel bad for doing this; no serious trader is actually using that guide and you may even end up haggling, but those who do use the guide will be grateful for the quick and easy transaction which lets them get back to their own preferred game.