I wouldn't "rescue" a pet from the pet store. They're not in good conditions there, but neither are dogs in the pound or cats in a cat shelter either. I find it baffling that people who work in pet stores and are supposed to be pet lovers too, allow this to happen.
Incidentally, when I went to the pound to rescue my oldest dog, I wasn't even there to get her. I was there to get another dog that my friends aunt had dropped off - because she too "couldn't take care of it any more". It was a golden retriever puppy, had all its shots, and was fixed and ready to go. My friend called me up frantic and said "you've been talking about getting a dog, this is perfect for you" so we hurried up there. However as we were walking from cage to cage, I saw this little coon mix puppy and picked her up and petted her for a bit, but that wasn't the dog so I put her back. Well when we finally found the golden retriever puppy, as soon as I picked him up the other one started wailing and howling. I totally melted, and put the golden retriever back and took her home instead, lol. But at the same time I was thinking, that retriever is gonna get snatched up by someone, as popular as they are.