Just a little bit of background, for those that may not know - Diamond/carpet crosses are a naturally occuring intergrade, which is fairly common knowledge. Comments about preserving the integrity of the species notwithstanding, it is a bit difficult to argue against it since Mother Nature has given it her blessing. Aside from that, there were "legitimate" reasons that the practice became common here in the States. Diamond pythons were outrageously expensive (no, that is not one of the "legitimate" reasons I mentioned, but I am sure it played a role also), and proved to be difficult to breed. Males tended to be disinterested in the concept, and many people were of the idea that one needed to maintain diamonds in different ratios than other snakes - where we typically keep several females for each male, the reverse of this became the logic du jour for diamonds. When that method found limited success, many breeders started putting proven Jungle carpets in with their females (or adding the female diamonds to their JC groups, as the case may have been). This, of course, worked; and the progeny were gorgeous and well received.
Another problem with diamonds was that individuals, and even entire collections were falling prey to a mysterious illness...characterized by brittle bones, poor muscle tone, and frequently respiratory infections that responded poorly to treatment. This became known simply as the diamond syndrome.
Now, back to the comments about 75% and 88% diamonds being passed of as pure. Most of the 75% diamonds I have seen have been easily discernible as crosses (I say most in case some stellar specimen slipped through unrecognized). As for the 88%ers, a common argument that I have read goes something to the effect of: If some of these are unknowingly introduced to the gene pool, how much impact will it really have if the recipients breed them true?
Besides, since diamonds and carpets interbreed in nature, how can you ever be sure that the founding stock is 100% pure anyway?
*edit* My apologies to the ball python people - I thought this thread was in a different forum. While my post adheres to the general topic at hand, it is better suited to discussion in a more generalized forum.
H.