I want to know the answer to the following question:
In some countries there is no formal deal but what that makes prosecuting bribes difficult?
All the background I'm provided with is that "In addition, there is often no such formal deal but only a mutual understanding, for instance when it is common knowledge in a municipality that to obtain a building permit one has to pay a "fee" to the decision maker to obtain a favorable decision.". Is that enough to answer the question?