There are a number of criteria at play, but nothing is perfect. Rest assured that if one gets banned for a shill, an email can usually clear things up. Generally those cases are rare.I use a VPN quite often as well. Not so much recently since I'm searching for a better provider but once I find one I like almost every bit of traffic will go through it.
Often a pm will be sent requesting info on multiple logins. Matches on previously banned accounts raise eyebrows.