No — and here is why.
I cannot guarantee that which I cannot control. Simple.
In order for a certain “result” to take place, numerous variables have to come together. No person has control over those variables. I know I cannot control the actions of the police, district attorney, judge, jury, client, witnesses, investigators, experts, etc., to reach a certain result. How can I possibly, in good conscience, guarantee that which is dependent on factors outside my control? I can’t control the results, but I can control the process.
We have control over the process in that we have choices along the way. We can choose to do A, B, C, etc., and help to bring about the desired results. I have faith that if I give my absolute best effort in everything I do, I give myself the best chance of obtaining the best results. So, the answer for me is not to guarantee the results, as I have no control over them, but to give the process my best, as that is the only thing over which I have control.
The way I see it, I have a duty to myself to do the best that I can in everything I pursue. This approach provides my clients with the best chances to gain the desired results.