I recently was at trade tables to advise somebody if the trade was good or not. During the trade at the last second, the other trader, who had 13,000 shells on the table said: "let me give you something free" his chat covered the shells numbers. He added a flower but at the same time removed the shells. I know how it's done, but only reporting how it's done to admins. Pictures below: (the person the picture is not the scammer, he's just my friend who discovered it from the scammer.)
http://i.imgur.com/HkDnYxn.jpg
http://i.imgur.com/lGq2PaP.jpg
http://i.imgur.com/Sj4VAXZ.jpg
Also, iMoney was the scammer. He was in disguise but I added him and he changed his name & look later.