It depends is usually the begining of the answer to most dog training questions. How do I get my dog to do X? how do I get my dog to stop doing X? Someone told me I should do X with my dogs, is that right? The reason for this is that most times we need more information. Tell me more about your specific situation and I can properly answer the question.
We also need to work with the dog they have. All dogs are individuals and we serve them best by remembering that. What may work for one dog in one home may not work for another. This is one reason I like doing the private sessions over group classes with people. Don't get me wrong, I think group classes are very valuable. You get to work with your dog around the distractions of other dogs and can also socialize them. (if allowed and appropriate) I send people to puppy classes in the area all the time. So many problems can be avoided later with the proper beginning.
It depends is also sometimes the answer to the question "Is this problem fixable?"
All problems may not be solvable within a specific context. If you have a dog that is not tolerant of other dogs in your home or you have a dog that bites people, yes you may be able to change their behavior. However many things come into play in those scenarios. Your lifestyle, and the time you have to address those issues. Not to mention the ability to manage the situation to keep everyone safe as we take the time to address the behavior. Not every dog belongs in every home. Sometimes it's simply a mismatch of energy levels. Fortunatly we have reputable breeders willing to take back dogs, shelters, and breed rescues that are available to help rehome the dogs when needed.
I think rescues (groups/shelters) are sometimes hard on owners who surrender dogs. In a job where you continually see people doing stupid stuff (throwing animals out ot moving cars and the like) is it hard not to become biased towards the human race. Do enough rescue work and you tend to start thinking most people suck. Not to mention how often rescue workers are lied to. When compassion fatigue sets in it is hard to stay positive. When I first became a trainer, from a rescue background, it was hard to admit that sometimes a dog just wasn't the right match for a home. But as a trainer it is easy to see that sometimes that is the case.
So if you ever ask trainer a question and want a good answer, be prepared to answer their follow up questions first. Keep in mind that very little is cut and dry in dog behavior. If it were there would certainly be far fewer books written on the subject! Just like the rest of life, adjustments need to be made for each situation. Why would we expect anything different in life with our dogs?