The scammer advertises in Local:
Checking the on the market you'll see the price the item is, usually, a couple of hundred million ISK more than what is being offered. In this case the Kronos is 1.27b ISK and the scammer is offering it for a flat 1 billion ISK
What Happens Now
The scammer states a trade in system because this is one way they can con a person by providing as little detail as possible, they can drag/drop a Kronos into the window and wait for the mark to enter the money then quickly swap it out for a Megathron (same hull, vastly cheaper ship at 177m).
By avoiding the use of the contract system the scammer can control the flow and easily show, with one hand, what is on offer then quickly substitute it with something else before accepting. Once complete there is no public trasnaction that shows the con, only the mark having less ISK and the scammer a larger wallet.
Confirming the Scam
There was a small, miniscule, possibility that this was a legitimate offer so I eve mailed the scammer and asked if they'd accept via contract and they said yes:
Except no contract was ever created and all of a sudden they "made a sale" and decreased the number available in their advertisement.
How Can You Protect Yourself
Rule #1 in Jita is: anything in Local is a scam to take your ISK.
If anyone offers you something but says they want to trade in station then this should instantly have alarms ringing in your head. Never, ever, do a trade within a station. Always insist on a contract where the details can be clearly set out showing what you will get in return for your money.
Block the scammer and move on.