You need a catchy name that people will remember and a location people shop in anyway. You want them to walk by and stop to see what kind of books you sell, they will keep it in their mind for for themself or a friend they that is a bookaholic.

A book store where I live sells paperback romance novels and people can trade one for another. People can bring in romances and that number of books is put in a notebook or comp showing how many books that person can get before they have to start paying again. Trust me, I used to be addicted to paperback romances. When I got rid of all my books I told them to add the credit to someone that reads alot.
I wouldn’t suggest the credit system for other kinds of books besides romance novels because 9 times out of 10 the person bought them for their own collection.