I'm still new to this but, in any breeding there is still no guarantee that you will get the outcome that you want. There are so many variables and with a het not being visual I would see it also as a buyers gamble. I have though about buying a couple hets but when I do, I still know there is a chance I would like the outcome. If there is a question, then as someone else posted, breed to a visual instead of het to het.
Just my feelings from a buyer point of view.
On a seller side, you will never be able to make everyone happy all the time, but you should be reasonable to rectify the situation if you guarantied the sale.