There is no way for them to know from the data they get, for example if I set my home computer up as a VPN router for my use they would be completely unable to know if I was at home or in Timbuktu. There is a general lookup table they try to compile of paid VPN IP addresses, it's pretty imperfect at best and with something like Tor it's completely useless (although Tor would be verrrry slow to trade on!). I kind of laugh when I see anyone using IP addresses as a form of security because it's such childs play to circumvent them that anyone who had a clue what they were doing could....and anyone incapable of circumventing them is not savy enough to be any threat...therefore they are entirely pointless.Also, most times, most businesses know the difference between a VPN IP address and a non-VPN IP address. IOW, most times, they can know who's on a VPN ... if they care.
