Okay...I'll be the "bad" guy and say something here. If you do not have a specific condition, medical or mental, and if your dog does not perform specific tasks to help you deal with or, in some cases, survive, that condition, then your dog is not suited to be labeled a service dog.
The ADA and service dog organizations have taken great measures to enable service dogs to accompany their handlers everywhere possible. It would be reprehensible to 'fake' having a service dog to avoid paying flight fees.
While there is no one agency "certifying" service dogs, there is a clear description of what a service dog should be in the ADA's literature.
One link here ADA Requirements for Service Animals
The ADA and other agencies have fought hard for the rights of disabled people with service dogs to get access to all public places for those dogs. We, as fellow humans, should not do anything to undermine that effort for the sake of saving money, or bypassing hotel rules for pets. It diminishes the real importance of what a service animal does for its handler.
You might be thinking of an emotional assistance dog, which is different than a service dog, for your fear of flying. You should ask your psychiatrist about that one. My sister has an emotional assistance dog for her depression in dealing with breast cancer. The little guy has done wonders for her.
Just something to think about before you go ahead. Believe me, I would LOVE to have Pepper certified as a service dog so I could take him everywhere, but the fact is...he's not a service dog, he's my beloved pet.