I have heard this scenario many times over the years. Her dog was aggressive and a trainer told her that "she needed to show it who is boss" and she believed him. She dropped her dog off in the care of this "dog trainer" that assured her that her problems would be solved when she picked her dog up.
Two weeks later she went to pick her up and to her horror her dog was not only still aggressive, but was visibly shaken and scared. This trainer used choke chains, "shake cans" and alpha rolls and surprise, surprise, caused her dog to be more fearful and aggressive.
There are no quick fixes in dog training! So many people want to ship their dog off to someone and get back a dog that is "fixed". It usually isn't that simple. When a dog is fearful (fear and aggression usually go hand in hand) doing things to that dog that cause more fear or pain are often times not going to work!
Depending on the dog, you can get a "false reading" of success by scaring a dog into not giving signals any longer. This is accomplished by abusing (trainers often call this "correcting") a dog when they growl, snap or bite. Then the dog becomes scared to show signals, but is not "cured". You can end up with a dog that seems to attack out of nowhere because they don't tell the world when they are scared, they just seem to snap.
Before I get a flood of comments from good, positive reinforcement trainers, I AM NOT saying that all board and train options for dogs are abusive. There are plenty of wonderful trainers doing great work with dogs that are in their care. But, unfortunately there are a lot that do abuse dogs.
If you want to send your dog for training, do your homework, watch the trainer, check references and trust your instinct. If something sounds too good to be true, it probably is.