Some of the best rat breeders have worked on "fixing" the American high white strain for decades, so far, some have had limited success by outcrossing every generation with "safe" rats to minimize the megacolon losses. Most high white morphs are truly beautiful rats and most grow up to be healthy if they don't go south as pups...
Bad things still happen for the people that really know what they are doing, I can't imagine how badly this will go wrong for someone who doesn't have a clue.
But to be honest, when we took our high white out in public she instantly drew a crowd, people that didn't even like rats instantly fell in love with her... sure after about 10 minutes everyone was playing with and meeting Fuzzy Rat, but when people first saw us Amelia got all of the attention. People are always going to want high whites and someone is always going to breed them. It's sad, but I can see the temptation. Knowing our Amelia and her brother were culled at about 3 weeks old, I wasn't very tempted to breed her. She grew huge and had sleek lines, in her prime she would have showed extremely well, but being a litter of two, both with striking markings, found in a feeder bin, I couldn't help but wonder what happened to the rest of her siblings. I could easily imagine someone finding her and her brother in the feeder bin and thinking they hit the jackpot.
Perhaps if you forward a link to the megacolon article it might help the byb choose more wisely, but sadly people usually play with fire until they get burned.
Best luck.