From personal experience, pups can change so much upto 8 weeks old (and of course after). When i viewed Taz at 3 weeks, his coat looked perfectly fine to me. At 8 weeks when i collected him, he had developed a little cowlick each side of his torso. Its not noticeable now, but he would have never been suitable for showing. I guess had i have wanted him for showing/breeding i would have pulled out of the sale, but he was never intended to be for either purpose.
I would therefore give a definate no to the week old pups.