I had a situation similar to @elbrant. I contacted a breeder wanting to get on a list for a puppy. She said she had a 16 month female that was available -she was going to SHOW but changed her mind. I said I had my heart set on a puppy and she said “the puppy stage is short- lived and there were a lot of advantages of getting a young dog that was past the puppy stage - you should at least come and meet the dog.” Needless to say it was love at first sight - she immediately bonded w/ my husband curling up next to him. Years later the breeder stated to me that she knew we were the right family for the dog - that she had only seen 2 times when one of her dogs immediately bonded with a family. I always said “ Kembe chose us.” In hind sight it was a blessing - I got a dog that was potty trained, could walk on leash, and already knew basic commands. My only regret is that I did not get her a sibling so that she had a companion. You shouldn’t have any issues. Congratulations- look forward for great adventure and happiness with your new basenji.
It was a little tongue-in-cheek my comment about the Basenji looking "pudgy". All 3 dogs appeared well fed. (or hey.... maybe the painter used fat brushes.... 😛 )
That was the extent of my "analysis".
Registration papers should be proof, but without DNA confirmation one can never be positive. I know a breeder (in another breed) who was getting old and a bit confused and I am sure some of her pups' parents were not accurately attributed, but the pups were purebred, just possibly from different sire. Coat colour can vary tremendously and it's more likely when it isn't a disqualification in the breed. If you are buying a dog described as purebred then there should be registration papers given to you. A DNA test should tell you whether the dog is Basenji or mixed with something else, if you really want to know.