Client wants .story (unpublished files) - do they need this?

The other thing to consider is this:  how comfortable are you with your client handing your source files over to another freelancer to modify, duplicate, repurpose and sell etc?  How comfortable are you with the potential for your client to take your source files, learn your methods (e.g. how do you get the interaction to behave in a certain way) and establish their own freelance business?  Don't underestimate the skills you have in using the software and the value this creates.  Anyone can buy a camera but it doesnt make them a photographer, same with Storyline.   If your client wants source files, i don't think it's a hard and fast rule that they can or can't, but should definitely be charged more. In graphic design land the standard is 300% more for source files.