Let me answer this, because this is an ISA Brown thread. You are concerned, if I understand it correctly, that someone might try and pawn off run-of-the-mill sex links as ISA Browns? I'm sad to say, it happens all the time. I have no idea why people aren't honest about it, but sadly, in too many cases, they are not. Why they think the ISA name lends them some marketing power or identity for their non-ISA birds is a mystery, but that is what people do. Sad and unnecessary.
Again, the ISA Brown, is a patented, commercial bird. Townline Hatchery, in Zeeland, MI is the only licensed seller that I know of. There may be more, but not too many. Commercial birds are carefully sold to protect the reputation of the genetics corporations that produce them. The ISA Brown is hardly the only such patented, commercial, brown egg layer out there. There are many others.