If you don't mind, can I point out a couple of things you did wrong?
First, it seems you didn't familiarize yourself with the store, the workers, or the owners.
Second, seems you hadn't established a relationship with the above named people.
Third, since there is no relationship then the only thing between you and them is formality, in effect you've become a salesmen and/or walking telemarketer for yourself which I doubt was your intent
Fourth, seems you approached them from the standpoint of "What can your bookstore do for me?". Again, that may not have been your intent but based on your description of their responses, that is how you probably came across to them.
So what is the fix?
Well, for this bookstore and others, sorta do the reverse of the above list. Familiarize yourself with the key staff, understand WHO you need to schmoooze with
Get on a first name basis with them and give them your business, i.e. you should be buying books from them. This establishes a business relationship. Similarly, refer them business and make sure they know you have refered them business. In fact, after you've established that relationship, it wouldn't hurt to have some friends come by and say, "Hey, my friend *your name* sent me over here..."
Once you have a relationship established with them, THEN you start talking about you being a writer and can they help you promote your book.
You can also pitch it as a prestige thing for THEM. I mean, it is nice to have a real life author come in to your shop and do a book signing, gives an establishment a sorta business/prestige feeling. In fact, perhaps you could tie into some of their promotions, offer to run a workshop explaining what it is like being a writer, writing that first book, etc. etc.
Again, notice how its not so much what they can do for you, but what you can do for them as well.
Anyways, just my two cents on this matter.
Take or leave as you see fit
Mel...