There are many dog trainers out there and there is no regulation for dog trainers. Anyone can claim as a “dog trainer” and become one. However, be aware what type of methods they use before you hire a dog trainer.
Fear motivation/Domination: This type of trainers uses domination, physical force and often use punishment. Dogs might obey due to fear. Dogs might seem well behaved but they could shut down, give up, or might go into depression. Some dogs may become more anxious and aggressive.
Positive reinforcement: This type of trainers teaches dogs one easy step at a time using treats to let them know when the dog did well and set them up for success. Dogs will be eager to learn more and very happy.
Everyone has freedom to choose, but I do recommend latter type. There is The Certification Council for Professional Dog Trainers® (CCPDT®) and you can find a certified dog trainer there.