As of now, whenever you purchase an item in the Grand Exchange through the "shop" interface, you will be presented with a confirmation screen. This screen will show you the item you're about to buy or sell, along with the amount and price.
This measure should prevent any mistakes people might make if they click the wrong item or the wrong amount, or if others try to scam them by swapping the price and amount - a popular scam that's been happening to several people in the past week. For example, someone would put up an offer for 1,000,000,000 toxic blowpipes for 1 coin each, leading people to believe someone was buying one toxic blowpipe for one billion coins and end up selling their blowpipe for just one coin.
We have done our best to refund anyone who had fallen prey to this scam lately. If you were a victim of this scam but have not yet been refunded, please contact me or Pikachu on Discord.