I'm creating a justice system in my game, and need help with one thing (so far :P). The players have the choice to rob shops, and their choice to do so reduces the shop's overall profits and therefore increases the tax to a region. If they're caught the shopkeeper won't serve customer again until they pay some compensation based on how much money they were going to steal, and they recieve a fine from the government (town guards will also attack people with unpaid fines and stuff).

Anyways, my concern is that players could get around this system by creating other characters and using them to do their shopping. I think I could stop players doing this by doing these two things (both of which I don't know how to do >.>):

1) Only allowing 1 player per IP to log into the game, no acceptions.
2) Perhaps creating a list of known associates (as ranter suggests) and lowering people's social status based on their friends' criminal activities. But how could I do this? And to what extent should I punish people for having poor liasons? It would be unfair to send guards after them afterall...