Can one try things on in a shop even though he has no intention of buying, I’m asking by a case of a Jew and also by a non-Jew. If not, when I’m like 90 percent sure I’m not going to is that also not allowed.
If there is chance, even a remote one, that you might buy the dress, then it is permitted to try it on. The storeowner wants you to try it on as there is a chance that you will get convinced to actually buy it. However, if you have absolutely no intention to buy it, (you are trying it on just in order to take a picture) then it is not allowed, as it would be geneiva.