Improper Format Attempted Scam

A man by the name of Toasty Zonda (http://steamcommunity.com/id/zondaf11/?textMessage=inviteSucceeded) attempted to scam me earlier today at about 9:00 eastern U.S. timewhile i was playign team fortress 2.
I was talkign to him on the server because i saw he was selling buds. I asked him if he would take a strange machina and some keys. He traded me so we could discuss in trade chat... Once we entered trade, he put up 3 clean buds. I put up my machina and asked him how many keys he wanted me to add, he said 5, i counteroffered 3 and he said: "i guess i can take it". As i was putting up the agreed 3 keys, he quickly switched out his 3 clean buds with one gifted bud and clicked ready (i didnt realize they were gifted at the moment). So i clicked my ready to trade box and on my way to click the trade button i coincidentally hovered over his bud where i thought i saw something, i looked again and sure enough, it was gifted. I told him i saw it was gifted and he left the server immediately.

I know i got lucky this time but i fear that his slick ways will end up screwing over someone else, so please help prevent this from happening.
Thank you,
Alfonze Frankenferno

ok, thank you for next time, safdly thought it happened too fast to get any screenshots or chat bc it was in game inside trade and i didnt know it was a scam till the last sec`ond and he ran immediately after