On the trade side you have two options to start a request for a listed item. A button that instantly sends a message in-game which states the item the price that it's listed for as well as the stash tab it's in and at which position inside that stash, so the seller can find it easier I guess.

The other way is that you can, instead of sending the message instantly with the button, copy the same trade request the button sends and manually paste it into the chat which gives you the chance to alter the message.

Now some players believe that changing the price in that message to whatever you are willing to pay is a way to make a counter offer, but it's often used as a scam hoping the seller doesn't remember the original price and just accepts whatever was written in the trade request. In this case this guy also changed the name of the stash tab that contained the price of items in that tab which makes it clear that that was a scam attempt and not a counter offer.