I might be wrong but usually with a het there arn't many markers. If your buying from a credited breeder I doubt they are looking to rip you off. If its just some random dude then I would be a little leery seeing how they probably want more than $100, which is usually the asking price for 2 normals. Sometimes there are bp's called Ringers that ppl sell. Usually they come from WC shipments and look basically like normals but have subtle light bands that can, when bred out, produce Pieds.