We've had this dicussionn many times in the reptile trade and I'm pretty sure fish are similar (except travelling in some instances) - in the wild reptiles don't travel THAT far from the place they were born, so the chances of them simply following pheromones to the nearest mate will lead them to at least a distantly related family member a good 50% of the time, so there is also quite a bit of inbreeding in wild populations of anything. I have even seen peoples' WC-fish here and you can clearly see defects from inbreeding in some of them. We don't encourage it, but A.) it's hard to know who is related and who isn't, and B.) most people agree that you tend to see problems at around 6-7 generations of inbred genetics. If you are going to do it, try not to do it a 2nd time and always at least LOOK for different bloodlines before settling on inbreeding. Captive fish already have kind of a rather diluted lineage already, sadly.
My vote is avoid when you can, but if you HAVE to, just do it once and always inform buyers if they are inbred so they can make their own call when it comes time for them to breed as well.
