I think one of the big problems with selling dog mixes is opening the door to a bunch of lies or at least misleading consumers. That said I have a mixed breed dog (PitbullxVisla) that is a rescue and by far the smartest, best dog I have ever had. I agree if you want a mix go rescue one and not open the door to scamming puppy mills. Not that they are all going to be like that but there are enough of them to be concerned.
A snake combo on the otherhand is much more obvious and distinguishable to the educated consumer(who is most likely to purchase a high priced snake). We also dont have public facilities full of ball python morph combos being put to sleep daily. When I rescued my dog 4.5 years ago the city of Los Angeles was exterminating 250 dogs a day. That is a very sad fact.