Some people don't know the values of items. New players should not be reported for making what they think is a good trade.
You should only report if you fall victim to a scam or are a target of a scam.
Please make sure you know the difference between an actual scam and someone just not meeting the value you have placed on your item(s). Trades you simply do not agree with should NOT be reported.
This is an example of a scam: Someone promises to give you $50 in Wallet credit if you give him an unusual.
This is not an example of a scam: Someone offers 1 key for your unusual.
Please don't report anyone for a trade offer that they have made unless it is actually a scam. A scam will always involve lying in some way, and it will usually involve trading something that is not in the trade window. If it is just a bad offer, just decline it and move on.