I do not know what you paid, and they are too young to tell quality, except to say that none have vaulted skulls. I would express displeasure as the one with yellow legs is CERTAINLY not pure silke, and for the sake of the sellers reputation, she should be willing to exchange that chick or at...
I do not think the seller is pulling your leg; it is far more likely that she is uninformed, and has birds that originated from a hatchery (either they or their parents). THere are many breeds with yellow legs, so I would not automatically assume cochin. Look at the wing feathers--are they...