If you decide to take this lad, you have to go into it with yours eyes wide open. Several things to bear in mind:
1. Dogs R Us are a pet retailer which usually means that the pups come from puppy farms. Puppy farm dogs tend to have (but not always) more ailments and medical problems which may be develop later on in life, due to poor breeding. The 'papers' are most likely useless bits of paper.
2. A 6 mo untrained dog might be far worse than a puppy - particularly if he has not been properly socialised around humans and other dogs. He may, for example, not have been taught not to use his teeth on humans and still be 'puppy biting' but with very sharp teeth. You are likely to have to go back to basics with toileting, basic training, socialisation, etc. If he is untrained, he will be entering his 'terrible teens' stage without the foundation of good training.
3. Lots of people tell the biggest whoppers when they are rehoming their dog. However nice the people may seem when you go to see them, don't base your decision on anything they say, but on your own views on the dog and the worse case you think you can cope with. Also the dog may be on his 'best behaviour' - i.e. they have just taken him for a walk to wear him out, just fed him, etc.
Very good luck with whatever you decide and I really hope the lad finds a good home - with you, hopefully, but for your sake, only if you are prepared for the difficult issues.
