You can say its because you want to know what name to give the snake. reptile people do it all the time, its really not a big deal. I pop or probe (if i'm able) anything I'm selling or trading unless the buyer doesn't care about sex. (and even then i usually still know since I've had the animal). I ALWAYS ask the seller to pop for me, and then I'll often pop it myself in front of the seller.
I have yet to get an "inbetween" animal, with mine there are either hemipenes, or not. (or with the geckos, BIG bulges , or not lol)