“If the guy really did not know, then the fault is with the guide. I could see charging the dentist a large fine.”
If the fault is with the guide, why should the dentist pay a fine?
Because there is a loss to the country — an injured party — caused by the dentist whether he meant to or not. If you accidentally injure someone’s property, even if you do not know it is their property, you are liable. If you buy someone’s property and it turns out to be stolen, you are liable to return the property. At the level of financial liability, not knowing is not an excuse.
If you harm someone’s property or take it on purposes, you are guilty of a crime such as vandalism or theft. If you do not know, you still have financial liability.