Something similar happened to me though I was lucky enough that the amount was small. The scammer had a perfect execution of his plan which trapped me. Last week, someone impersonated me to one of my clients, luckily he was able to identify the scammer.
Nice to hear you were lucky not to fall for this scam!!
Btw, so how is it that these guys are knowing your contacts of business because these aren't people that are disclosed to the public... Unless these people start with those funny messages in the official chat group of who do I contact for marketing purposes etc and when directed to the right person they now execute their scams and impersonation...
I suppose besides the Admins don't PM you first, I think bitcointalk PM authentication should help clean this mess, unless chat history exists then one can keep the conversation going.