To be the best working team that you can be, you should train in all different situations, thereby acclimating your dog to every possible situation he may encounter. Also train with different people, take seminars, etc. In other words, take your training to the highest levels possible.
To be a reputable team, when it comes time for that certification, certify yourself and your dog, with a third party, neutral person, or organization, that is knowledgeable of working dogs in your chosen discipline. If you certify with anyone that you regularly train with, that only gives the appearance of “favoritism.”
Every reputable K-9 organization that I have ever been associated with, calls for neutral, third party evaluators, as well as “double blind” evaluations, to truly test the competence of the team being tested. When your regular trainer tests you, this just gives the appearance of “favoritism.”
With double blind evaluations, you really know that you and your dog are working together as a team. You should NEVER know the location of hides or subjects on certifications. This just leads to the handler cueing the dog into giving his indication, for fear that you may miss something. But if you are afraid that the dog may miss something, then the real question is, are you really ready for certification? If so, then perhaps you need more training before attempting that certification.