When looking for dog a dog trainer, no matter what area of dog training, make sure you research the company you are wanting to hire.
There are many one man/woman businesses out there who will dazzle you with qualifications and listings and memberships and most of all LOW PRICES, however will not deliver when dealing with your dog, either the results you require OR the customer service that you expect.
The old saying - 'you get what you pay for' is literally that.
When dealing with a dog and behaviour issues, the trainer needs to have the confidence to deal with any dog, any situation and read the dog, its body language carefully, otherwise not only yours but the trainers' confidence will be completely lost.
Once confidence is lost, the dog will not respond to them and thats when things can go wrong. Then you will become a frustrated dog owner paying for a service that doesn't fix the problems.
Many people, including some trainers out there don't realise what a dog is actually capable of doing if they haven't ever seen it or dealt with it before.
Most dog trainers out there are self taught, therefore all of their work/knowledge will come with their experience - please ask as many questions as you can about the trainer you are about to hire, about their experience, not just about qualifications.
Good luck in searching for dog training and when you do find a good dog trainer, stick with them!