When I shop for a trainer "certification" means next to nothing. There are a few hands on programs that offer apprenticeships, but most places are a quick class and don't even require you to have a dog.
PetCo and
PetsMart, for example, boast "certified" trainers - it's a couple of short classes and TADA. I've only met a few who know even a minimum about dogs. My local
PetCo trainer takes her dog to my trainer.
Results are what matter to me. I want to see what you've accomplished. If I'm just looking for a "pet" class or basic obedience, I expect you to have put a CGC on a couple of dogs at a minimum. Not necessarily your dogs, but dogs you have trained. For more advanced classes, I would expect you to have more advanced titles, at least Rally Excellent. Again, you sh ould ideally be able to point to other dogs you have worked with or at a minimum references from owners you have worked with.
You said friends and family. Did YOU train/work the dogs or did you train the owner? Two VERY different scenarios. To be a good dog trainer, you have to not only know dogs but people. Then i'd want to see you in action, watch a class or training session and see how you interact with the dogs. I'd also want to know what experience you had working with my breed of dog.
For example, my trainer has several Rally and agility titles on her dogs. She has numerous clients who have titled dogs with her help - rally, obedience, and agility. She is cerified through AKC to do CGC testing. She has started several dogs into therapy work as well.