There is no need to cull healthy offspring.
Premium examples should command somewhat above market, nice examples market and poor examples below that, IMO. They all still get sold, and folks can breed them if they like.
The idea that you do not know if they are going to produce nice offspring is partially true. Two super nice Pastels may throw the occasional bad one when the genes just do not line up, but you are much more likely to get nice babies out of parents with nice genetic material in the first place. Not too many morphs throw truly random levels of a trait.
By the pure "even tho you have something that's top notch, doesn't mean ever one of it's offspring is going to be" mentality you negate the effects of line breeding.
In the end we are all giving out opinion. I will be honest ant tell someone that "I" would not buy a certain animal. They are coming here and asking for that opinion (for the most part) so they should be willing to hear it and make a decision on their own.