1. Displaying higher ad price and paying lesser.
This happens when the seller is not careful and might not observe it. You know that at the process of igniting a p2p trade if price changes, you would be notified and you will need to refresh to get the current price.
So, what some cheaters do is to display higher buy price in like 425 and when you click to trade, the figure will change to like 423 and if you are not careful enough you won't notice and continue with the trade at 423 instead of 425. Then, if they are caught they will claim that price changed, it is a smart way of cheating. So, to avoid this, ensure that the price displayed in adds in what is used in trade. You can do the calculations manually to ensure that it is matching with the amount of fiat you are expecting.