highly unlikely. extremely even lol
a breeder who sells wholesale could possibly sell his normals to a chain pet store, and might accidentally sell a pos het, but that would be careless, and once again - highly unlikely
u can always buy a normal dinker tho =D
which means theres something irregular about it that proves genetic, but not necessarily a morph. just something about it thats genetic
EDIT:
just adding a note in case ur one of those people who get defensive ;p
u KNEW they were POS hets, but i havent read about anyone saying they sell their pos hets to pet stores, i just figured ppl do it to get rid of norms and make room for holdbacks ;p