Your situation reminds me of a New York case involving the purchase of a Maltese. The purchaser claimed the dog was represented by the seller pet store as “teacup” Maltese. As time passed, the dog, Little Miss Muffet, weighed in at eight pounds, above the five pounds that is considered the weigh limit for a “teacup” Maltese. The court attributed the dog’s weight not to eating too much kibble, but rather to the genetic makeup of the dog, that she was a standard Maltese, not a “teacup.” The court awarded the purchaser the difference in price between a standard Maltese and “teacup” Maltese.
Oftentimes it is really difficult to tell what a mixed-breed dog is a mixture of, particularly as a puppy. Also, most landlords do not actually weigh dogs, but have a weight limit to keep away the larger breeds, a policy I don’t happen to like. Nevertheless, if your dog is within the 25-pound range, hopefully you will not have a problem with your landlord. I suggest you read your sales contract to see if it offers any remedies. I think it is unlikely that the contract would provide purchasers with any remedies if the mixed breeds indicated turns out to be wrong. I also doubt that you would be awarded any money in a case against the pet store based on your dog's weight or mixture of breeds. Most importantly, I hope you enjoy your dog whatever the mix of breeds he may be, and that he does not grow up to be the size of a Great Dane!