I don't know what things are like where you live (it would be pretty weird if I did), but here in LA, if you buy a dog from a store instead of rescuing one, everyone will know about it. It's a weird sixth sense that all Los Angelenos have; they'll know that you bought a dog from some "puppy mill," and they will hate you for it.
"He's cute, but he's CLEARLY from a store at the mall, so go fuck yourself."
When I started telling people I was looking for a dog, they would grab my shoulders and say, "Whatever you do, rescue one. Go to a shelter instead of a puppy mill. Promise me. PROMISE ME YOU WILL DO THIS!"
They're right, by the way. I don't usually publicly get behind causes of any kind because I don't want to ever come off as preachy, and I don't think anyone is "better" than anyone else, but rescuing a dog from a shelter is better than buying one from a store, and doing so will make you a better person. Shelters are where lost or abandoned dogs end up, and those are the dogs that need a home the most. They're not puppy mill dogs (usually adorable puppies that have been strictly trained and bred for adorableness), they're the dogs that are found wandering in the middle of the street, the dogs that are found in parking lots after they've been thrown out of moving cars (I learned from shelter owners that this is a shockingly common occurrence). It's easy for puppies to get purchased and difficult for dogs to get a second chance, which is why, as a result of over-dog-population, shelters are forced to put down unrescued dogs every single year (about 4 million annually).
So I decided I'd rescue a dog, because I wouldn't be paying some breeder or some puppy store at my local mall; I would be saving a dog that, without my enormous, gracious heart, would be tragically put down. "Rescuing" made me feel like a hero.
Also, I had it in my head that, since over-dog-population ("overpupulation?") was such a problem, my new dog would be free. Buying a dog from a dog seller is expensive because you're getting a brand new dog from a trusted breeder, and you'll accept the high price tag (some purebred Corgis can cost up to $1,000) because you're paying for the guarantee that your dog won't have any baggage or mange or weirdness. Your dog would have no skeletons in its closet; it would be perfect (despite being, you know, a Corgi).