Due to the recent spate of hackings, we now require a SYTHE PM confirming the Skype you're talking to in order for a scam report to be considered valid. This PM must be confirmed RIGHT before the transaction is initiated.
EDIT #1: Suggested PM: This is _____ trading you, ______ on my skype _______. I am trading _______ for _______. Speaking on Skype confirmed.
How about that? That way it's not an issue of how long the whole conversation of the trade is but rather a quick fix that people should PM right before you press the "accept" button for RS3GP, the "pay" button for Paypal, etc.
EDIT #2: Edit #1 is a bit of a long rule to implement.
EDIT #3: Let's put this in a scenario. You contact the person through Skype. You add each other and based off their Sythe profile, this is in fact their Skype and has not been reported as hacked. Now let's say it's a trade that requires some time to set up. You spend about half n hour to an hour setting everything up. Everything is ready to go. Now you ask for a PM confirmation before actually initiating the trade of risked goods. Once that PM confirmation is sent, you have now placed liability on that person's Sythe account if there is a scam that takes place.