If you check out their adoption process, this should give you a rough idea. Call them and ask about their "return policy." Rescues usually have the "forever home" in mind, whereas a shelter may just say "if the dog doesn't work out, just bring them back." Also, there are many internet groups dealing with rescue. Sign up for the breed groups you are interested in. You can get a good idea who is "reputable" within a few weeks. These are active rescuers and they are full of advice and know who's "naughty or nice." Those who are actively rescuing dogs are more likely to be reputable.

If you're a really busy person, I would advise against a puppy as you won't have time for him. Puppies take up a lot of time because you have to mold them into the right behaviors as they grow. What you probably should have is an adult dog. I'd recommend a low-energy breed that has already been housetrained and is friendly. Breeders sometimes have young adults for sale and then there are always rescues and shelters. If you decide to go with a breeder, make sure it is a reputable one.