There is by buying from a reputable breeder.
There are no real visual clues that will tell you animal is het for clown.
No there isn’t. You either have to know what the parents are or see if she throws a clown when bred. A normal het clown is pretty cheap anyway I’d just buy something definite instead of a possible.
As far as definitive no there is not. Kind of like pied markers they may present they may not, they can present in animals without pied at all. After speaking with John Dague Jdconstriction regarding some odd coloring and patterning in my DH Clown Axanthic clutch, he said it was common to see some oddness in the het clowns but nothing that is definitive or 100%.