Ultimately, isn't your order buying company the true bidder/buyer. I realize they are making the call on how much Brahman influence they are willing to accept, which in turn affects your buying tendencies, but they themselves are still making a call that may or may not be justified. They could just as easily tell you they want all black calves and that is making an assumption on an animal they know nothing about and may in fact perform worse than a Brahman influenced animal and this is all based on a wim.
Also, as far as hairing up, my cattle have no problems hairing up. In your case, you are taking an animal from the south and making them adjust in a short period of time. All animals will experience a shock under these conditions. Also, a Brahman influenced animal that is already in an environment that is "colder" shouldn't be discounted for that particular reason so in my opinion that excuse doesn't hold water for all Brahman influenced animals to be discounted. If it is a weather issue, then all cattle raised in the south should have a discount compared to cattle raised in Northern country. And in turn, shouldn't Bos Taurus cattle be discounted at certain times of the year when they will be experiencing the heat of summer.
Another point, there have been studies on Brahman influence cattle and there ability to perform in colder weather. It has been found that Brahman influenced cattle like Santas are able to perform in colder weather.
link:
http://jds.fass.org/cgi/reprint/39/6/715.pdf
My point is that many people assume that Brahman influenced cattle are inferior because they either can not perform in the feedlot, have poorer meat quality, etc. when that isn't always the case. I guess that's why the cattle we raise have to be just slightly better than the avg. cow to make up for the discrimination we sometimes receive at the sale barn.
One more point, do your buyers discount you for a Hereford calf that may have a blemished/scarred eye too? Does that blemished/scarred eye really affect their profitability when they are cutting him up? I really don't think it does. Buyers find any reason they can to get discounts and these discounts are not always justified.