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.

There is almost always an adoption fee. The places that house unwanted animals have to make money to feed them, shelter them, give them meds, doc visits, spay/neuter etc... the list goes on. The adoption fee, is to try to get enough money to keep doing these generous deeds. They rely solely upon donations and adoption fees. I'm not sure about a pound dog though. You may check. Of course you can always save a starving one from the streets as I did with my second dog. If money is super tight, you may need to be sure you can afford vet bills, and food, as that is my biggest household expense currently. Hope you find a great one and give it a wonderful home. So many animal badly need good loving homes.