The main issue here is deformities. As simple as it could be put, is the clownfish beautiful or not? I've seen TONS of nice patterns, even crazy patterns, on super ugly fish. Deformities could be genetic, transferred from parent to offspring, or environmental, due to the water quality while the clowns are being raised. There is still a huge cloud above these issues and its hard to get straight answers from breeders but here's my take. If there are two clownfish raised together in the same tank and thus same conditions and one of them has flared gills (an environmental deformity), the clownfish has a greater predisposition to flared gills. They both grew up in the same tank and water why would only one have flared gills? So even environmental deformities are not acceptable because I'm not sure if we know how much of a component of those deformities is a genetic predisposition to deforming under those environmental conditions.
Some deformities:
Gills - flared, too short, pushed up from underneath, gills exposed causes greater chance for bacterial infections
Jaw - crooked, overbite, underbite, circular, fused open, does this impede on their ability to eat
Fins - pelvic fins are the #1 to look at, pectoral fins can also be small, small dosal/tall dorsal, do they swim funny because of their fins
Swim bladder - can the fish swim properly and 'float' in the water column with minimal effort?
Body Shape - Is the fish ugly? is the belly pushed up or is the head pinched? broken and healed bones
General deformities - any imaginable deformity is possible, I've seen wild clownfish harvested with no tail, but living in the wild.
Growth rate - do they grow at an average pace, are they stunted, forever stunted genetics