General genetics question

Something that has come up many times on my facebook forums are ads for 100% Hets.
I'm a gecko person, so BP folks cut me some slack here. I own one single pet BP; it is black, brown, and yellow. I digress.

For a trait that is recessive (and not visible in a het), say albinism in green iguanas, to get a 100% het, one would have to breed a normal to an albino. Of course, if you went out and grabbed a wild green iguana, you could be pretty certain it's normal, but let's say we're working with a captive bred population. My question is, how could you be 100% certain that one of the parents was a normal and not a het? How many generations of testing do most people use to give them that certainty? Or do you just maintain a lineage back to the WC animal?

Thanks in advance for anyone who can clear this up for me!!!

Noelle