New York Times article:
https://www.nytimes.com/2017/09/21/s...g-trainer.html
They raise the point that owners need to verify credentials. Don't just take the trainer's word for it that they have the CPDT or IIABC or other certification.
Here are links to both Certification Council of Professional Dog Trainers and Association of Professional Dog Trainers:
CPDT/Certification Council for Professional Dog Trainers
Why you should look for a certified dog trainer - CCPDT
Association of Professional Dog Trainers:
https://apdt.com/pet-owners/