OFTEN!
Recently I weakened and bought ten chicks from the Cornishx bin. I do know what they look like, and loved that the staffer getting my chicks assured me that the two buff colored chicks were Cornishx too. She resented my comment that they weren't, but I'd get them anyway, as 'mystery chicks'. One is a buff Orphington, hopefully a pullet, and the other might be a hatchery RIR cockerel.
I got these, knowing who they weren't, and that's fine. It's bad when these folks sell birds who obviously aren't as advertised, and lie about them.
Mary