Do you trust Audiogon?

Drastic, I think you are right on point. It appears to be attempted wire fraud, too. It sucks when the crap flies start feeding. 

Looks like someone is getting a divorce and trying to hide some assets. If there is something illegal no one knows exactly what audiogon is doing. Generally federal authorities do not want anyone to take any action, leave things as they are until they can investigate which has always been my experience, so I wouldn't worry about audiogon. You did the right thing by ending the transaction and reporting. 

Banks (US at least) are required to report $10k and up transactions. The Feds can take a look at potential money laundering scams or other illegal activity. Breaking the sale up into smaller pieces is not illegal as far as I know.

Taking a sale off Audiogon is done to avoid paying fees to Audiogon. This is against their policy for obvious reasons but by no means uncommon especially on larger sales. It probably breaches their sales agreement - they could press charges but i doubt that is common. 

Neither of these concerns are huge to me. Audiogon didn’t respond to you because they see this every day and because even if they communicated with the seller they aren’t going to share it with you. 

Uncomfortable?  Cancel the sale, but from what we know at this point it is not worth the big hairy cow you are having. 

Buzzzzzzzzzzzz....