I have bought both types of kits. The kind with and without the pattern. So, I am used to asking the question to know if it is in there. I think the reason I enjoy the kitted fabrics with the patterns is, I live up out of town and it isn't always easy to find the great fabrics to make it special. Running from store to store to find fabrics isn't always productive either.
I have a couple self made "kits" I have started that need some fill in fabrics I need to find before I can make them. I have changed out fabrics in some ready made ones before too, like you girls. But, for the most part, I open the kits and check the contents for the correct sizes and fabrics right away. I don't like surprises in the middle of a snow storm. Or, to wait until the fabric is sold out and unavailable.
So, you are right. Don't assume anything when shopping for kits. I am happy the shop owner is gracious enough to share with you the pattern. Not all shop owners are that nice.