I would like to clarify, since this seems to have been assumed otherwise: I didn't say they wouldn't
flip seams at all if you're wearing a costume, I said that they would ask first
. (At least, they SHOULD ask first or give a polite forewarning, because it's very rude not to. And if the contestant refused, well, that would be a sign right there that things probably aren't finished very well!)
The majority of the cons I've competed at or judged at did not require contestants to be in costume during craftsmanship judging unless the judging was taking place literally right before the show or during the show, in which case the contestants need to be stage ready anyway.
Personally, I feel that if the craftsmanship judges are going to be watching the show, then it's no big deal if the contestant is not wearing the costume during judging - the judges will see them in the costume on the stage later anyway to gauge the overall project. But if it's a situation where the craftsmanship judges don't watch the actual show, then yeah, contestants really should be in costume otherwise there's no way for judges to gauge proper fit.
As a contestant, I prefer wearing my costume to judging but I'm not opposed to bringing it in on a hanger either. I've had to do it a few times.
As a judge, I kinda prefer when things aren't being worn because then I can really see them from the inside out.
(In most of the situations I've been in, on either side of the fence, the craftsmanship judges do watch the show.)