How not to get scammed
When trading someone there're many tools that you can use in order not to get scammed.
To check the price of a item or info about a item or to check someone's backpack use this site: http://backpack.tf/
If you wish to sell a item or check the real time prices of what people are paying use this site: http://www.tf2outpost.com
If you want to check to see if a person has been marked as a scammer use this site: http://steamrep.com/
If you wish to purchase items for real money use this site: http://forums.sourceop.com
You may also wish to check to see if the person is a reputable trader. In google type: sourceop <steam profile #>
To get a persons REAL steam profile number visit that persons steam profile page. Then copy the link of their profile to this site: http://steamidconverter.com
Look at the bottom for their profiles permalink. You want to do it this way because some scammers will set their custom url to a known reputable traders to try and confuse people.