In my humble opinion
popping is every bit as reliable as probing, at least with corns. It's also quicker and less stressful on the nervous hatchings. At least if you know how to do it. As mentioned before, don't do it on a snake more than a month or two old. Kathy Love's book describes the process as well as words could, but you really just need to do it on a known pair a few times until it becomes second-nature. I can pop a whole clutch in under 30 minutes. I pop when segregating them to their own cages right after hatching, and again (to double check) before selling.
I had the assistance of a very experienced prober this season and I caught two mistakes on his end, I was 100%. Perhaps on the second popping, I'll catch an error, but seldom do.
I'm not boasting about my abilities, just the accuracy of popping. For the record, I've sold lots (hundreds?) of snakes over the years and have never had anyone let me know I sold the a mis-sexed animal. Granted, many probably wound up as pets, but I think Rich, Kathy, Don Soderburg and most other big breeders would back me up on the merits of determining sex using this method.