Whatever company you use, make sure you check them out first. Just because they are a certified member of an organization, it does not guarantee their honesty http://capitalexhaust.com/index.php?id=11
If these are regular customers of yours, and the hood cleaner you chose messes up, it is going to be your name on the line. All I am saying is check in to them and don't take any certifications or memberships at face value.