Quote Originally Posted by alan1 View Post

correct, but - that would be 'mis-labeling' the animal

Of course, but it is a true statement that there would be a 66% chance that the animal was het for both traits in that hypothetical circumstance. This appears to be the only way that the seller (mentioned in the OP's post) could be telling the truth, however incomplete, about his/her 66% double hets. Breeding a DH to a DH will not get 66% DHs. This is what the OP was concerned about.