I wouldn't originally sell any hets that I didn't produce myself as 100% hets. I would sell them as "I bought these as 100% hets from so and so at this place on this date. I haven't proven them out yet." If they turn out to not be hets, I'd work with them and call the breeder to see what he says. If he offers anything I would pass it on to my buyer. I would probably charge less than what the average het is going for, but I'm being honest and I think that takes some liability off me. If I sell something as a guaranteed het and it proves to be normal, I think I'd owe a refund.