When you hire a lawyer or an attorney and he tells you, that you have a so called Slam Dunk Case it might be time to reconsider whether this is the right lawyer or not. Because usually cases aren´t that clear, also the law most often allows diffrent points of view and oppinions.
Surefire cases are very seldom! So you should ask yourself, is my case really that crystal clear? Are different perceptions of the case impossible? Is it really that bullet prove? Are there no other rational oppinions possible?
In case of doubt you might be better of asking a second lawyer for his oppinion.