Scamming Is Not Cool.
Scams is when player cheats another player and takes one or more of their valuable items. This is vary annoying for most people that are just trying to trade there hard earned goods. There're a few different types of scamming and its good to know what they are so you don't fall for them yourself.
This is someone that selects the item you want and then deselect the item hoping you didn't notice. This is the most conman type of scam and can be easily avoided by simply not trading with the person. If you see someone do this, just end the trade, block the person, and move on.
This is someone that pretends to "auction" items. Usually they'll ask you to give them your bid and they tell you that you'll get your stuff back if you don't win. This is not the case though because why should they? If they get your stuff there is so other force making them give it back to you. Its like telling a noob in godlands to hold you stuff for a minute while your AFK. If you see one of these people just block them.
This is someone who says they can dupe your inventory. They will tell you that they have some sort of program that can dupe any item and ask you to give them your items so they can dope them for you. They might even show you them "duping" an item, which is actually them just using a backpack. Really, a good way to catch a duper is to ask them to dupe a worthless item (t0/t1) and when they can't do it laugh in there face and report them.
This is a person that tricks you that one item is a different item by look. For instance, Fakers will use snake oil to impersonate Defence potions or use health potions as Vitality.