If the BB shell is for 30mm, it should just be a question of pressfit or threaded. However because you say you run a shimano crankset (presumable you mean 24mm?) before, that makes me think the BB shell is smaller, so a 30mm won’t fit? Or did you have adaptors in the BB for the smaller spindle?
Ah, reading what Chad posted above, looks like it should be a shell for a 30mm spindle. Go to a different shop.