The temperature thing does not seem to apply to cresties as far as can be determined so far. The gender ratio for crestie hatchlings seems to stay about 3 females to 2 males, or 60% female hatchlings for large populations. That gives you slightly better than even odds of getting females if you buy them too small for sexing. If you wait, your odds of getting males go up tremendously because breeders hold on to females more. Some breeders have pretty good ability to look at the preanal pores with a jeweler's loupe and determine sex before the "cresticles" develop, but in general most wait for the bulge.