It is not necessary to call the police if you've been a victim of this kind of fraud. Most problems will be easily resolved without the police. For example if someone has been using your card you can just contact your bank and you will get your money back (they will either make a chargeback or will have to pay you from their own money). Everything aboun checking your real identity is a problem of a service provider and you should never take any expences on it. Ofcourse you should check the background of the bounties you are  working on but do not take it too serious.