I believe the progamme is all about building self confidence in women who have little or no self confidence. The programme works because there is no trickery with surgery dental work etc such as 10 Years Younger.
Gok certainly has a way with words as he does seem to encourage even the most reluctant to part with their clothes.
The programme shows women in a good light and and it also shows what can be done with a little bit of knowledge, how to dress for your body shape, good hairstlye and makeup.
The window stunt would have been done with a select band of people, no kids, or those easily offended by female nudity. This was said in the commentray if you listen to it.
It also looked like a side street not a main road, so access of passers by could be controlled. There was also an awning on the building, so people from across the street probably couldn't see in from above the 1st floor. The reveal was at night so less likely to draw unwanted viewers.
This would all have been done with the consent of the shop, local council and probably the police.