I love my hermits. No problems whatsoever. And they do a great job cleaning the algae from in between polyps where it would be really tough for me to get to myself (or any other critter I know of). I did pick the least aggressive hermits available though (Mexican Red Tip/Leg).
They've done really well for me. Lots of extra shells. All snails still alive and kicking.

By the way according to Scott Michael's Marine Invertibrates Margarita snails are cool water snails and slowly perish in tanks with tropical temperatures.
Your hermit may indeed be doing their job by cleaning up your dying margaritas...