There are a couple of reasons why a dog doesn't listen to you
1. The dog doesn't understand what you are asking it to do
2. You don't have a high enough reward ( favorite toy, High quality meat)
3. There is something more "eye catching" to your dog. Another dog, a person, leaves on the ground, smells in the air or the ground.
Now why wouldn't your dog understand what you are asking?First of all It does take a number of repetitions for a dog to display that they actually know what going on. Just because my dog can sit occasionally doesn't mean that she knows how to truly sit.
Most times we think with our human brains instead of the dog's brain. We pick up on these ideas quick, but for the dog it takes time. Be patient.
Another reason your dog doesn't understand is because dogs don't generalize well. Therefore sitting at home does not equal sitting at the neighbor's house. Its important to practice commands at different locations.
The next problem is your dog doesn't want what you have. Most dog owners will use commercial treat brands of food. Illl see them training their dog and the dog will be semi enthused. The dog is probably saying in her head " Ill sit and ill take the treat but I'm not excited about it. Why not? Because your treats suck".
Imagine if the dog said this out loud. So many dog owners would take a huge blow to their ego. Another note, some dogs, especially working breeds, prefer to play with toys. My pit bull likes food, but he loves to play tug. This really get him going and focused on me.
Now finally we are discussing dealing with distractions. My advice is to take it slow when increasing distractions. First start with getting your dog to down in front of his favorite toy, then in front of another object they like.
Next you can get them to down while a stranger is around, then a dog. This is just a simple straightforward example of how to progress with distractions. A dogs nose will lead the way so its important that you don't let a dogs sniff the ground unless you give your release word. This is for every dog but especially hounds.
All three reasons tie into each other. For example, in the face of distraction it is vitally important to have something your dog wants since you are competing for their attention. Also the dog has to thoroughly know what you are asking automatically. If they haven't done the command a few hundred times it is not wise to try it in the face of distractions. We want to set our dog up to succeed. Therefore we want to challenge them, but not give them something too difficult.