If done properly, yes, a crystal can be glued into place and offer some water resistance, although I typically sleep better at night with those which are held in place with a gasket, as glue deteriorates faster over the long term compared to a gasket . Gluing an oversized crystal into a watch that was supplied with a gasketed crystal is a cheap/easy way around ordering genuine parts and doing it the best way possible. If you feel you paid for the best way possible and did not receive it, I'd go talk to the jeweler/watchmaker. BTW, was this a "jeweler" or a "watchmaker"? Jewelers do not receive the same training on repairing watches that watchmakers do, unless they have gone through such additional education/training beyond their "jeweler" training. I have no idea if his credentials are sufficient- do you?