Declined 76561198001943444 (Mars.)

Victim:
steamID: [G4F] GG_PLS
steamID32: STEAM_0:0:43397170
steamID64: http://steamcommunity.com/profiles/76561198047060068
customURL:
steamrepURL: http://steamrep.com/profiles/76561198047060068

Scammer:
steamID: Mars.
steamID32: STEAM_0:0:20838858
steamID64: http://steamcommunity.com/profiles/76561198001943444
customURL:
steamrepURL: http://steamrep.com/profiles/76561198001943444

Screenshots:
http://i.imgur.com/nvZU3.png

Description:

First of all, sorry for my bad english.... But i really dont want others get scammed like me . I have traded with this guy several time then he asked me to become a partner ... He promised me if i give him all my common items (DOTA 2) he would return me back for 1-2 Rare Items in 1 or 2 days. . At first i have gave its to him, but later i have changed my mine and asked him to give me back all my items... Then he cut off all contact and Unfriend me ...

Do you have a screenshot of the chat?

Sorry Sir.... But i dont have it. I didnt think he was a Scammer at first . Because this guy seems like has some good reputation as those "Recommended Trader" comments on his profile page ( dont know those are fake or he just made its up with his friends...). When he went offline i was only thought he just got some Connection problem like the last time i have traded with him....accept that he never show up again and Unfriend me.... As you can see i am New here and New on Steam and i didnt know how to report a Scammer at first ... Therefore, i didnt know the importance of Screen Chat for reporting Scammers....

Sorry but isnt the screenshot of "Trade History" and screenshot of Him being no longer friend with me still enough ? I have seen the "Acceptable Format" before posting this and i was thought i couldnt report this guy without a Screenshot of the chat ... but i saw a Guide on the Forum saying that i still can report him with the Screenshot of Trade History which is showed i have actually gave him all those items...

It is required, but in and of itself is not enough simply because of the fact there is no way to verify what the original agreement. Hypothetically speaking, it could have been a Paypal transaction, or something of the sort. Without a way to verify that this was indeed the case, there is nothing that can be done.